dfs的优化

#include<bits/stdc++.h>
using namespace std;
int i, j, n, ans = 0;
bool vis1[20], vis2[20], vis3[20];
char mp[100][100];

inline void dfs(int x){
	if (x == n + 1){
		ans++;
		return;
	}
	for (int i = 1; i <= n; ++i){
		if (vis1[i])continue;
		if (vis2[x + i - 1])continue;
		if (vis3[n + x - i])continue;
		if (mp[x][i] == '.')continue;
		mp[x][i] = '.';
		vis1[i] = 1;
		vis2[x + i - 1] = 1;
		vis3[n + x - i] = 1;
		dfs(x + 1);
		mp[x][i] = '0'; 
		vis1[i] = 0;
		vis2[x + i - 1] = 0;
		vis3[n + x - i] = 0;
	}
}
int main(){
	int i, j;
	cin >> n;
	for(i = 1; i <= n; ++i){
		for(j = 1; j <= n; ++j){
			cin >> mp[i][j];
		}
	}
	dfs(1);
	cout << ans;
return 0;
}