From 083de051cbc88f391c6bd28481b856013e293ce9 Mon Sep 17 00:00:00 2001 From: Simon Tatham Date: Mon, 29 Mar 2021 20:49:17 +0100 Subject: [PATCH] Filling: remove directional bias in grid generation. The method of generating a solved Filling grid (before winnowing clues) is to loop over every square of the board, and for each one, if it has a neighbour which is part of a different region of the same size (i.e. the board is not currently legal), fix it by merging with one of its neighbours. We pick a neighbour to merge with based on the size of its region - but we always loop over the four possible neighbours in the same order, which introduces a directional bias into the breaking of ties in that comparison. Now we iterate over the four directions in random order. --- filling.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/filling.c b/filling.c index a62161a..ffa3ab1 100644 --- a/filling.c +++ b/filling.c @@ -414,10 +414,15 @@ retry: int merge = SENTINEL, min = maxsize - size + 1; bool error = false; int neighbour, neighbour_size, j; + int directions[4]; + + for (j = 0; j < 4; ++j) + directions[j] = j; + shuffle(directions, 4, sizeof(int), rs); for (j = 0; j < 4; ++j) { - const int x = (board[i] % w) + dx[j]; - const int y = (board[i] / w) + dy[j]; + const int x = (board[i] % w) + dx[directions[j]]; + const int y = (board[i] / w) + dy[directions[j]]; if (x < 0 || x >= w || y < 0 || y >= h) continue; neighbour = dsf_canonify(dsf, w*y + x);