循环8皇后

这回不会爆栈了，但是效率很低，O(n^2)的时间复杂度，需要优化

#include <stdio.h>

#define N 10
int q[N+1] = {0};
int cnt = 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;

    //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() {
    int i=0;
    while (i <= N) {
        if (q[i] < N-1) {
            q[i] +=1;
            break;
        }

        q[i] = 0;
        i++;
    }

    return;
}

int main(int argc, char* argv[]) {
    while (q[N] == 0) {
        int i;

        for (i=0; i<N; i++) {
            if (!can_put(i, q[i])) break;
        }

        if (i == N) {
            cnt++;
            print_q();
        }

        next_qn();
    }

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

    return 0;
}