8皇后问题

8皇后问题太经典了，各种算法书解释回溯都用这个例子，下面是求解8皇后问题的代码：

#include <stdio.h>static int count;#define QUEEN_NUMBER 8#define NO_QUEEN -1#define TRUE 1#define FALSE 0#define ABS(x) ((x)>0?(x):(-(x)))int conflict(int *queen, int pos){int i;for (i = 0; i < pos; i++) {if ((queen[i] == queen[pos]) || ABS((queen[i] - queen[pos])) == ABS(i - pos)) return TRUE;}return FALSE;}void try_next(int *queen, int pos){if (pos == QUEEN_NUMBER) {count++;return;}int i;for (i = 0; i < QUEEN_NUMBER; i++) {queen[pos] = i;if (!conflict(queen, pos)){try_next(queen, pos + 1);}}}void foo(void){count = 0;int queen[QUEEN_NUMBER];int i;for (i = 0; i < QUEEN_NUMBER; i++) {queen[i] = NO_QUEEN;}try_next(queen, 0);printf("count = %d\n", count);}int main(int argc, const char *argv[]){foo();return 0;}

运行结果是8皇后问题共有92个解。