再次优化过的8皇后问题

#include <stdio.h>

#define N 9 
int q[N] = {0};
int not_end = 1;
int trace = 0;
int cnt = 0;
int sum = 0;

void print_q() {
    int i;

    for (i=0; i<N; i++) printf("%d ", q[i]);

    printf("\n");

    return;
}

int can_put(int m, int n) {
    int i,j;

    sum++;

    //row is ok
    //colume
    for (i=0; i<m; i++) {
        if (q[i] == n) return 0;
    }

    //left-up
    for (i=m-1,j=n-1; i>=0 && j>=0; i--,j--) {
        if (q[i] == j) return 0;
    }

    //right-up
    for (i=m-1,j=n+1; i>=0 && j<N; i--,j++) {
        if (q[i] == j) return 0;
    }

    return 1;
}

void next_qn() {
    while (trace >= 0) {
        if (q[trace] < N-1) {
            q[trace] +=1;
            break;
        }

        q[trace] = 0;
        trace--;
    }

    if ( trace < 0) {
        not_end = 0;
    } else {
        int i = trace + 1;
        while (i < N) {
            q[i] = 0;
            i++;
        }
    }

    return;
}

int main(int argc, char* argv[]) {
    while (not_end) {
        int i;

        for (trace; trace<N; trace++) {
            if (!can_put(trace, q[trace])) break;
        }

        if (trace == N) {
            cnt++;
            //print_q();
            trace--;
            next_qn(N-1);
        } else {
            next_qn();
        }
    }

    printf("CNT: %d, times: %d\n", cnt, sum);

    return 0;
}

CNT: 352, times: 72378

real    0m0.007s
user    0m0.004s
sys    0m0.000s