123 lines
2.8 KiB
C
123 lines
2.8 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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static void setpval(struct sudoku *sud, unsigned r, unsigned c, uint16_t pval)
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{
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for (unsigned val = 0; val < NDIGITS; ++val) {
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if (pval & 1) {
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update(sud, r, c, val);
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return;
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}
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pval >>= 1;
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}
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}
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int solve(struct sudoku *sud)
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{
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unsigned r, c, n, i, j, val, sr, sc;
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bool match;
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uint16_t valmask, pvals;
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for (n = 0;; ++n) {
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match = false;
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for (r = 0; r < NDIGITS; ++r) {
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for (c = 0; c < NDIGITS; ++c) {
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if (DET(sud->cells[r][c]))
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continue;
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/*
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* Check if there's only one possible value this cell
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* can have.
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*/
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pvals = sud->cells[r][c] & PVALSMASK;
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for (val = 0; val < NDIGITS; ++val) {
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if (pvals & 1) {
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if (pvals == 1) {
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update(sud, r, c, val);
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match = true;
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goto next_cell;
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}
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break;
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}
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pvals >>= 1;
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}
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/*
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* Check if there's a possible value unique to this
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* cell in its row.
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*/
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valmask = 0;
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for (i = 0; i < NDIGITS; ++i) {
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if (i != r && !DET(sud->cells[i][c]))
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valmask |= sud->cells[i][c];
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}
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if ((pvals = sud->cells[r][c] & ~valmask)) {
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setpval(sud, r, c, pvals);
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match = true;
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continue;
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}
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/*
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* Check if there's a possible value unique to this
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* cell in its column.
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*/
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valmask = 0;
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for (i = 0; i < NDIGITS; ++i) {
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if (i != c && !DET(sud->cells[r][i]))
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valmask |= sud->cells[r][i];
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}
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if ((pvals = sud->cells[r][c] & ~valmask)) {
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setpval(sud, r, c, pvals);
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match = true;
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continue;
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}
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/*
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* Check if there's a possible value unique to this
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* cell in its segment.
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*/
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sr = SEGLEN * (r / SEGLEN);
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sc = SEGLEN * (c / SEGLEN);
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valmask = 0;
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for (i = sr; i < sr + SEGLEN; ++i) {
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for (j = sc; j < sc + SEGLEN; ++j) {
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if ((i != r || j != c) && !DET(sud->cells[i][j]))
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valmask |= sud->cells[i][j];
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}
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}
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if ((pvals = sud->cells[r][c] & ~valmask)) {
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setpval(sud, r, c, pvals);
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match = true;
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continue;
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}
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next_cell:;
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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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