mirror of
git://git.tartarus.org/simon/puzzles.git
synced 2025-04-21 16:05:44 -07:00
Introduce a new deductive mode in Slant's Hard level, which is the
generalisation of the previous deduction involving two 3s or two 1s either adjacent or separated by a row of contiguous 2s. I always said that was an ugly loop and really ought to arise naturally as a special case of something more believable, and here it is. The practical upshot is that Hard mode has just become slightly harder: some grids generated by the new Slant will be unsolvable by the old one's solver. I don't think it's become _excessively_ more hard; I think I'm happy with the new difficulty level. (In particular, I don't think the new level is sufficiently harder than the old to make it worth preserving the old one as Medium or anything like that.) [originally from svn r6591]
This commit is contained in:
Simon Tatham
263
slant.c
263
slant.c
@ -24,6 +24,7 @@
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#include <stdio.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <stdlib.h>
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#include <stdarg.h>
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#include <string.h>
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#include <string.h>
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#include <assert.h>
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#include <assert.h>
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#include <ctype.h>
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#include <ctype.h>
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@ -272,6 +273,27 @@ struct solver_scratch {
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*/
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*/
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signed char *slashval;
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signed char *slashval;
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/*
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* Stores possible v-shapes. This array is w by h in size, but
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* not every bit of every entry is meaningful. The bits mean:
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*
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* - bit 0 for a square means that that square and the one to
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* its right might form a v-shape between them
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* - bit 1 for a square means that that square and the one to
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* its right might form a ^-shape between them
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* - bit 2 for a square means that that square and the one
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* below it might form a >-shape between them
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* - bit 3 for a square means that that square and the one
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* below it might form a <-shape between them
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*
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* Any starting 1 or 3 clue rules out four bits in this array
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* immediately; we can rule out further bits during play using
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* partially filled 2 clues; whenever a pair of squares is
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* known not to be _either_ kind of v-shape, we can mark them
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* as equivalent.
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*/
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unsigned char *vbitmap;
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/*
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/*
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* Useful to have this information automatically passed to
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* Useful to have this information automatically passed to
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* solver subroutines. (This pointer is not dynamically
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* solver subroutines. (This pointer is not dynamically
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@ -289,11 +311,13 @@ static struct solver_scratch *new_scratch(int w, int h)
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ret->border = snewn(W*H, unsigned char);
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ret->border = snewn(W*H, unsigned char);
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ret->equiv = snewn(w*h, int);
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ret->equiv = snewn(w*h, int);
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ret->slashval = snewn(w*h, signed char);
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ret->slashval = snewn(w*h, signed char);
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ret->vbitmap = snewn(w*h, unsigned char);
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return ret;
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return ret;
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}
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}
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static void free_scratch(struct solver_scratch *sc)
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static void free_scratch(struct solver_scratch *sc)
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{
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{
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sfree(sc->vbitmap);
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sfree(sc->slashval);
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sfree(sc->slashval);
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sfree(sc->equiv);
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sfree(sc->equiv);
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sfree(sc->border);
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sfree(sc->border);
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@ -388,6 +412,36 @@ static void fill_square(int w, int h, int x, int y, int v,
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}
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}
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}
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}
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static int vbitmap_clear(int w, int h, struct solver_scratch *sc,
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int x, int y, int vbits, char *reason, ...)
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{
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int done_something = FALSE;
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int vbit;
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for (vbit = 1; vbit <= 8; vbit <<= 1)
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if (vbits & sc->vbitmap[y*w+x] & vbit) {
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done_something = TRUE;
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#ifdef SOLVER_DIAGNOSTICS
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if (verbose) {
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va_list ap;
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printf("ruling out %c shape at (%d,%d)-(%d,%d) (",
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"!v^!>!!!<"[vbit], x, y,
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x+((vbit&0x3)!=0), y+((vbit&0xC)!=0));
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va_start(ap, reason);
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vprintf(reason, ap);
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va_end(ap);
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printf(")\n");
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}
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#endif
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sc->vbitmap[y*w+x] &= ~vbit;
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}
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return done_something;
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}
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/*
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/*
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* Solver. Returns 0 for impossibility, 1 for success, 2 for
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* Solver. Returns 0 for impossibility, 1 for success, 2 for
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* ambiguity or failure to converge.
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* ambiguity or failure to converge.
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@ -426,6 +480,11 @@ static int slant_solve(int w, int h, const signed char *clues,
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*/
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*/
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memset(sc->slashval, 0, w*h);
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memset(sc->slashval, 0, w*h);
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/*
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* Set up the vbitmap array. Initially all types of v are possible.
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*/
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memset(sc->vbitmap, 0xF, w*h);
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/*
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/*
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* Initialise the `exits' and `border' arrays. Theses is used
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* Initialise the `exits' and `border' arrays. Theses is used
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* to do second-order loop avoidance: the dual of the no loops
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* to do second-order loop avoidance: the dual of the no loops
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@ -453,69 +512,6 @@ static int slant_solve(int w, int h, const signed char *clues,
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sc->exits[y*W+x] = clues[y*W+x];
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sc->exits[y*W+x] = clues[y*W+x];
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}
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}
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/*
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* Make a one-off preliminary pass over the grid looking for
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* starting-point arrangements. The ones we need to spot are:
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*
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* - two adjacent 1s in the centre of the grid imply that each
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* one's single line points towards the other. (If either 1
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* were connected on the far side, the two squares shared
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* between the 1s would both link to the other 1 as a
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* consequence of neither linking to the first.) Thus, we
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* can fill in the four squares around them.
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*
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* - dually, two adjacent 3s imply that each one's _non_-line
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* points towards the other.
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*
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* - if the pair of 1s and 3s is not _adjacent_ but is
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* separated by one or more 2s, the reasoning still applies.
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*
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* This is more advanced than just spotting obvious starting
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* squares such as central 4s and edge 2s, so we disable it on
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* DIFF_EASY.
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*
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* (I don't like this loop; it feels grubby to me. My
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* mathematical intuition feels there ought to be some more
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* general deductive form which contains this loop as a special
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* case, but I can't bring it to mind right now.)
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*/
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if (difficulty > DIFF_EASY) {
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for (y = 1; y+1 < H; y++)
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for (x = 1; x+1 < W; x++) {
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int v = clues[y*W+x], s, x2, y2, dx, dy;
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if (v != 1 && v != 3)
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continue;
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/* Slash value of the square up and left of (x,y). */
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s = (v == 1 ? +1 : -1);
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/* Look in each direction once. */
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for (dy = 0; dy < 2; dy++) {
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dx = 1 - dy;
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x2 = x+dx;
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y2 = y+dy;
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if (x2+1 >= W || y2+1 >= H)
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continue; /* too close to the border */
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while (x2+dx+1 < W && y2+dy+1 < H && clues[y2*W+x2] == 2)
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x2 += dx, y2 += dy;
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if (clues[y2*W+x2] == v) {
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#ifdef SOLVER_DIAGNOSTICS
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if (verbose)
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printf("found adjacent %ds at %d,%d and %d,%d\n",
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v, x, y, x2, y2);
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#endif
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fill_square(w, h, x-1, y-1, s, soln,
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sc->connected, sc);
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fill_square(w, h, x-1+dy, y-1+dx, -s, soln,
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sc->connected, sc);
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fill_square(w, h, x2, y2, s, soln,
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sc->connected, sc);
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fill_square(w, h, x2-dy, y2-dx, -s, soln,
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sc->connected, sc);
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}
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}
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}
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}
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/*
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/*
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* Repeatedly try to deduce something until we can't.
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* Repeatedly try to deduce something until we can't.
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*/
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*/
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@ -837,6 +833,147 @@ static int slant_solve(int w, int h, const signed char *clues,
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}
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}
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}
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}
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if (done_something)
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continue;
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/*
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* Now see what we can do with the vbitmap array. All
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* vbitmap deductions are disabled at Easy level.
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*/
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if (difficulty <= DIFF_EASY)
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continue;
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for (y = 0; y < h; y++)
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for (x = 0; x < w; x++) {
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int s, c;
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/*
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* Any line already placed in a square must rule
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* out any type of v which contradicts it.
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*/
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if ((s = soln[y*w+x]) != 0) {
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if (x > 0)
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done_something |=
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vbitmap_clear(w, h, sc, x-1, y, (s < 0 ? 0x1 : 0x2),
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"contradicts known edge at (%d,%d)",x,y);
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if (x+1 < w)
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done_something |=
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vbitmap_clear(w, h, sc, x, y, (s < 0 ? 0x2 : 0x1),
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"contradicts known edge at (%d,%d)",x,y);
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if (y > 0)
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done_something |=
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vbitmap_clear(w, h, sc, x, y-1, (s < 0 ? 0x4 : 0x8),
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"contradicts known edge at (%d,%d)",x,y);
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if (y+1 < h)
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done_something |=
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vbitmap_clear(w, h, sc, x, y, (s < 0 ? 0x8 : 0x4),
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"contradicts known edge at (%d,%d)",x,y);
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}
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/*
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* If both types of v are ruled out for a pair of
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* adjacent squares, mark them as equivalent.
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*/
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if (x+1 < w && !(sc->vbitmap[y*w+x] & 0x3)) {
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int n1 = y*w+x, n2 = y*w+(x+1);
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if (dsf_canonify(sc->equiv, n1) !=
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dsf_canonify(sc->equiv, n2)) {
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dsf_merge(sc->equiv, n1, n2);
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done_something = TRUE;
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#ifdef SOLVER_DIAGNOSTICS
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if (verbose)
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printf("(%d,%d) and (%d,%d) must be equivalent"
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" because both v-shapes are ruled out\n",
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x, y, x+1, y);
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#endif
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}
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}
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if (y+1 < h && !(sc->vbitmap[y*w+x] & 0xC)) {
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int n1 = y*w+x, n2 = (y+1)*w+x;
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if (dsf_canonify(sc->equiv, n1) !=
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dsf_canonify(sc->equiv, n2)) {
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dsf_merge(sc->equiv, n1, n2);
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done_something = TRUE;
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#ifdef SOLVER_DIAGNOSTICS
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if (verbose)
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printf("(%d,%d) and (%d,%d) must be equivalent"
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" because both v-shapes are ruled out\n",
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x, y, x, y+1);
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#endif
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}
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}
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/*
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* The remaining work in this loop only works
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* around non-edge clue points.
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*/
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if (y == 0 || x == 0)
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continue;
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if ((c = clues[y*W+x]) < 0)
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continue;
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/*
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* x,y marks a clue point not on the grid edge. See
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* if this clue point allows us to rule out any v
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* shapes.
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*/
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if (c == 1) {
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/*
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* A 1 clue can never have any v shape pointing
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* at it.
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*/
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done_something |=
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vbitmap_clear(w, h, sc, x-1, y-1, 0x5,
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"points at 1 clue at (%d,%d)", x, y);
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done_something |=
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vbitmap_clear(w, h, sc, x-1, y, 0x2,
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"points at 1 clue at (%d,%d)", x, y);
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done_something |=
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vbitmap_clear(w, h, sc, x, y-1, 0x8,
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"points at 1 clue at (%d,%d)", x, y);
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} else if (c == 3) {
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/*
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* A 3 clue can never have any v shape pointing
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* away from it.
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*/
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done_something |=
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vbitmap_clear(w, h, sc, x-1, y-1, 0xA,
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"points away from 3 clue at (%d,%d)", x, y);
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done_something |=
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vbitmap_clear(w, h, sc, x-1, y, 0x1,
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"points away from 3 clue at (%d,%d)", x, y);
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done_something |=
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vbitmap_clear(w, h, sc, x, y-1, 0x4,
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"points away from 3 clue at (%d,%d)", x, y);
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} else if (c == 2) {
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/*
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* If a 2 clue has any kind of v ruled out on
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* one side of it, the same v is ruled out on
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* the other side.
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*/
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done_something |=
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vbitmap_clear(w, h, sc, x-1, y-1,
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(sc->vbitmap[(y )*w+(x-1)] & 0x3) ^ 0x3,
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"propagated by 2 clue at (%d,%d)", x, y);
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done_something |=
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vbitmap_clear(w, h, sc, x-1, y-1,
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(sc->vbitmap[(y-1)*w+(x )] & 0xC) ^ 0xC,
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"propagated by 2 clue at (%d,%d)", x, y);
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done_something |=
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vbitmap_clear(w, h, sc, x-1, y,
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(sc->vbitmap[(y-1)*w+(x-1)] & 0x3) ^ 0x3,
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"propagated by 2 clue at (%d,%d)", x, y);
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done_something |=
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vbitmap_clear(w, h, sc, x, y-1,
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(sc->vbitmap[(y-1)*w+(x-1)] & 0xC) ^ 0xC,
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"propagated by 2 clue at (%d,%d)", x, y);
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}
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#undef CLEARBITS
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}
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} while (done_something);
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} while (done_something);
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/*
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/*
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Reference in New Issue
Block a user