From 168cdd8e8e00e66808a584218c5e9fa97bce51d0 Mon Sep 17 00:00:00 2001
From: Camden Dixie O'Brien <cobrien@witekio.com>
Date: Sun, 9 Mar 2025 09:53:14 +0000
Subject: [PATCH] Add simple contradiction-driven search mechanism

Gets an about 6% improvement
---
 main.c | 76 +++++++++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 73 insertions(+), 3 deletions(-)

diff --git a/main.c b/main.c
index 9c1bf1a..aca745e 100644
--- a/main.c
+++ b/main.c
@@ -104,6 +104,70 @@ static update_res_t update(state_t *state, int *x_out, int *y_out)
 	return FOUND_NOTHING;
 }
 
+static update_res_t
+search_at(state_t *state, int x, int y, int *x_out, int *y_out)
+{
+	update_res_t res;
+
+	state_t with_mine;
+	memcpy(&with_mine, state, sizeof(state_t));
+	with_mine.field[x][y] = MINE;
+	do {
+		int res_x, res_y;
+		switch (res = update(&with_mine, &res_x, &res_y)) {
+		case FOUND_MINE:
+			break;
+		case FOUND_SAFE:
+			with_mine.field[res_x][res_y] = SAFE;
+			break;
+		case FOUND_NOTHING:
+			break;
+		case FOUND_CONTRADICTION:
+			*x_out = x;
+			*y_out = y;
+			return FOUND_SAFE;
+		}
+	} while (res == FOUND_MINE);
+
+	state_t with_safe;
+	memcpy(&with_safe, state, sizeof(state_t));
+	with_safe.field[x][y] = SAFE;
+	do {
+		int res_x, res_y;
+		switch (res = update(&with_safe, &res_x, &res_y)) {
+		case FOUND_MINE:
+			break;
+		case FOUND_SAFE:
+			with_safe.field[res_x][res_y] = SAFE;
+			break;
+		case FOUND_NOTHING:
+			break;
+		case FOUND_CONTRADICTION:
+			state->field[x][y] = MINE;
+			return FOUND_MINE;
+		}
+	} while (res == FOUND_MINE);
+
+	return FOUND_NOTHING;
+}
+
+static update_res_t search(state_t *state, int *x_out, int *y_out)
+{
+	for (int y = 0; y < HEIGHT; ++y) {
+		for (int x = 0; x < WIDTH; ++x) {
+			if (state->field[x][y] != UNKNOWN)
+				continue;
+
+			if (countadj(state->field, x, y, UNKNOWN) != MAX_ADJ) {
+				update_res_t res = search_at(state, x, y, x_out, y_out);
+				if (res == FOUND_MINE || res == FOUND_SAFE)
+					return res;
+			}
+		}
+	}
+	return FOUND_NOTHING;
+}
+
 static status_t solve(int *turns_out)
 {
 	state_t state = { .mines = 0, .unknown = WIDTH * HEIGHT };
@@ -123,7 +187,8 @@ static status_t solve(int *turns_out)
 		update_res_t res;
 		do {
 			res = update(&state, &x, &y);
-			assert(res != FOUND_CONTRADICTION);
+			if (res == FOUND_NOTHING)
+				res = search(&state, &x, &y);
 		} while (res == FOUND_MINE);
 
 		if (check(state.field) != OK) {
@@ -169,12 +234,17 @@ int main(void)
 		}
 	}
 
+	if (nincorrect > 0) {
+		printf(
+		    "Fail: %d incorrect! (%0.1f%%)\n", nincorrect,
+		    (double)nincorrect / NRUNS);
+		return 1;
+	}
+
 	const double solved_prop = (double)nsolved / NRUNS;
-	const double incorrect_prop = (double)nincorrect / NRUNS;
 	const double first_prop = (double)nfirst / NRUNS;
 	const double solved_safe_start_prop = (double)nsolved / (NRUNS - nfirst);
 	printf("Solved %d (%0.1f%%)\n", nsolved, 100 * solved_prop);
-	printf("%d incorrect (%0.1f%%)\n", nincorrect, 100 * incorrect_prop);
 	printf("%d died on first turn (%0.1f%%)\n", nfirst, 100 * first_prop);
 	printf("%0.1f%% solved on safe start\n", 100 * solved_safe_start_prop);