Camden Dixie O'Brien
f51e9a06b0
- Bits 0-8 are the possible values - Bits 9-12 is the concrete value - Bit 15 is 1 if the cell is determined
111 lines
2.5 KiB
C
111 lines
2.5 KiB
C
/*
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* Copyright (C) 2022 Camden Dixie O'Brien
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU Affero General Public License as
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* published by the Free Software Foundation, either version 3 of the
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* License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Affero General Public License for more details.
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*
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* You should have received a copy of the GNU Affero General Public
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* License along with this program. If not, see
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* <https://www.gnu.org/licenses/>.
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*/
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#include "solve.h"
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#include <stdio.h>
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int solve(struct sudoku *sud)
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{
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unsigned r, c, n, i, j, val, np, pr, pc;
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bool match;
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uint16_t valmask;
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for (n = 0;; ++n) {
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match = false;
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/* Check if only one place a value can go on each row. */
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for (r = 0; r < NDIGITS; ++r) {
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for (val = 0; val < NDIGITS; ++val) {
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valmask = 1 << val;
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np = 0;
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for (c = 0; c < NDIGITS; ++c) {
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if (!(sud->cells[r][c] & DETMASK)
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&& sud->cells[r][c] & valmask) {
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pr = r;
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pc = c;
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++np;
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if (np > 1)
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break;
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}
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}
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if (np == 1) {
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if (update(sud, pr, pc, val) != OK)
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return -1;
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match = true;
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}
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}
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}
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/* Check if only one place a value can go on each column. */
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for (c = 0; c < NDIGITS; ++c) {
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for (val = 0; val < NDIGITS; ++val) {
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valmask = 1 << val;
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np = 0;
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for (r = 0; r < NDIGITS; ++r) {
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if (!(sud->cells[r][c] & DETMASK)
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&& sud->cells[r][c] & valmask) {
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pr = r;
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pc = c;
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++np;
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if (np > 1)
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break;
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}
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}
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if (np == 1) {
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if (update(sud, pr, pc, val) != OK)
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return -1;
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match = true;
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}
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}
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}
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/* Check if only one place a value can go in each segment. */
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for (i = 0; i < NDIGITS; ++i) {
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for (val = 0; val < NDIGITS; ++val) {
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valmask = 1 << val;
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np = 0;
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for (j = 0; j < NDIGITS; ++j) {
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r = SEGLEN * (i / SEGLEN) + j / SEGLEN;
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c = SEGLEN * (i % SEGLEN) + j % SEGLEN;
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if (!(sud->cells[r][c] & DETMASK)
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&& sud->cells[r][c] & valmask) {
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pr = r;
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pc = c;
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++np;
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if (np > 1)
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break;
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}
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}
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if (np == 1) {
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if (update(sud, pr, pc, val) != OK)
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return -1;
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match = true;
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}
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}
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}
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/* Exit if no matches. */
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if (!match)
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return n;
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}
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}
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