| @@ -4,6 +4,8 @@ |
| 4 | 4 | * Because everyone on the SkyTrain is doing these now and I refuse |
| 5 | 5 | * to do them by hand. -- ksimpson, may 2005 |
| 6 | 6 | * |
| 7 | * fast branch: bitmasks instead of scanning. -- zz9 |
| 8 | * |
| 7 | 9 | * usage: sudoku [puzzle.txt] |
| 8 | 10 | * puzzle is 9 lines of 9 chars, digits or '.' for blanks |
| 9 | 11 | */ |
| @@ -14,23 +16,31 @@ |
| 14 | 16 | static int grid[9][9]; |
| 15 | 17 | static long nodes = 0; |
| 16 | 18 | |
| 17 | | static int ok(int r, int c, int v) |
| 19 | static unsigned short rows[9], cols[9], boxes[9]; |
| 20 | |
| 21 | #define BOX(r, c) (((r) / 3) * 3 + (c) / 3) |
| 22 | |
| 23 | static void place(int r, int c, int v) |
| 18 | 24 | { |
| 19 | | int i, br, bc; |
| 25 | grid[r][c] = v; |
| 26 | rows[r] |= 1 << v; |
| 27 | cols[c] |= 1 << v; |
| 28 | boxes[BOX(r, c)] |= 1 << v; |
| 29 | } |
| 20 | 30 | |
| 21 | | for (i = 0; i < 9; i++) { |
| 22 | | if (grid[r][i] == v || grid[i][c] == v) |
| 23 | | return 0; |
| 24 | | } |
| 25 | | br = (r / 3) * 3; |
| 26 | | bc = (c / 3) * 3; |
| 27 | | for (i = 0; i < 9; i++) { |
| 28 | | if (grid[br + i / 3][bc + i % 3] == v) |
| 29 | | return 0; |
| 30 | | } |
| 31 | | return 1; |
| 31 | static void unplace(int r, int c, int v) |
| 32 | { |
| 33 | grid[r][c] = 0; |
| 34 | rows[r] &= ~(1 << v); |
| 35 | cols[c] &= ~(1 << v); |
| 36 | boxes[BOX(r, c)] &= ~(1 << v); |
| 32 | 37 | } |
| 33 | 38 | |
| 39 | static int ok(int r, int c, int v) |
| 40 | { |
| 41 | return !((rows[r] | cols[c] | boxes[BOX(r, c)]) & (1 << v)); |
| 42 | } |
| 43 | |
| 34 | 44 | static int solve(int pos) |
| 35 | 45 | { |
| 36 | 46 | int r, c, v; |
| @@ -44,10 +54,10 @@ |
| 44 | 54 | for (v = 1; v <= 9; v++) { |
| 45 | 55 | nodes++; |
| 46 | 56 | if (ok(r, c, v)) { |
| 47 | | grid[r][c] = v; |
| 57 | place(r, c, v); |
| 48 | 58 | if (solve(pos + 1)) |
| 49 | 59 | return 1; |
| 50 | | grid[r][c] = 0; |
| 60 | unplace(r, c, v); |
| 51 | 61 | } |
| 52 | 62 | } |
| 53 | 63 | return 0; |
| @@ -87,6 +97,7 @@ |
| 87 | 97 | int main(int argc, char **argv) |
| 88 | 98 | { |
| 89 | 99 | FILE *f = stdin; |
| 100 | int i; |
| 90 | 101 | |
| 91 | 102 | if (argc > 1 && !(f = fopen(argv[1], "r"))) { |
| 92 | 103 | perror(argv[1]); |
| @@ -96,6 +107,10 @@ |
| 96 | 107 | fprintf(stderr, "sudoku: need 9 rows\n"); |
| 97 | 108 | return 1; |
| 98 | 109 | } |
| 110 | for (i = 0; i < 81; i++) { |
| 111 | if (grid[i / 9][i % 9]) |
| 112 | place(i / 9, i % 9, grid[i / 9][i % 9]); |
| 113 | } |
| 99 | 114 | if (!solve(0)) { |
| 100 | 115 | printf("no solution (are you sure you copied it right?)\n"); |
| 101 | 116 | return 1; |
