HDU 2553 N皇后问题(DFS)

/*************************************************************************
    > File Name: E.cpp
    > Author: 
    > Mail: 
    > Created Time: 2017年11月26日 星期日 10时51分05秒
 ************************************************************************/

#include <iostream>
#include <cstring>
#include <cstdio>
using namespace std;

#define MAX_N 11
typedef long long ll;
ll ans[20];
int vis1[MAX_N * 3], vis2[MAX_N * 3], vis3[MAX_N * 3];
int n;

bool check(int x, int y) {
    return (!vis1[x + y] && !vis2[y - x + n] && !vis3[y]);
}
void setPoint(int x, int y) {
    vis1[x + y] = vis2[y - x + n] = vis3[y] = 1;
}
void movePoint(int x, int y) {
    vis1[x + y] = vis2[y - x + n] = vis3[y] = 0;
}
int dfs(int x, int cnt, int n) {
    if (cnt == n) {
        return 1;
    }
    int total_num = 0;
    for (int j = 0 ; j < n ; ++j) {
        if (!check(x, j)) continue;
        setPoint(x, j);
        total_num += dfs(x + 1, cnt + 1, n);
        movePoint(x, j);
    }
    return total_num;
}
int solve(int x) {
    memset(vis1, 0, sizeof(vis1));
    memset(vis2, 0, sizeof(vis2));
    memset(vis3, 0, sizeof(vis3));
    return dfs(0, 0, x);
}
void init() {
    for (int i = 1 ; i < MAX_N ; ++i) {
        ans[i] = solve(i);
    }
}
int main() {
    init();
    while (scanf("%d", &n) != EOF) {
        if (n == 0) break;
        printf("%lld\n", ans[n]);
    }
    return 0;
}