POJ 1321 棋盘问题（dfs）

解析：

[code]#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <cstdlib>
using namespace std;
typedef long long ll;
const int INF = 0x3f3f3f3f;
const int N = 15;
char grid

;
bool vis
;
int n, k, ans;
void dfs(int row, int cur) {
    if(cur == k) {
        ans++;
        return ;
    }
    if(row >= n) return ;
    for(int j = 0; j < n; j++) {
        if(!vis[j] && grid[row][j] == '#') {
            vis[j] = true;
            dfs(row+1, cur+1);
            vis[j] = false;
        }
    }
    dfs(row+1, cur);
}
int main() {
    while(scanf("%d%d", &n, &k) != EOF) {
        if(n == -1 && k == -1) break;
        memset(grid, 0, sizeof(grid));
        memset(vis, 0, sizeof(vis));
        for(int i = 0; i < n; i++) {
            scanf("%s", grid[i]);
        }
        ans = 0;
        dfs(0, 0);
        printf("%d\n", ans);
    }
    return 0;
}