Guarding the Chessboard UVA - 11214 

https://vjudge.net/problem/UVA-11214

刚开始直接对棋盘进行操作，直接T到死

代码借鉴别人的

这道题如果采用常规的判重操作，时间是承受不住的，因为每次都要对一百个点进行判重

因为这个又T了好几次

另外从样例中可以看出放5个是最多的，所以如果前4个不行，直接输出5即可

#include<iostream>
#include<cmath>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<iomanip>
#include<assert.h>
#include<vector>
#include<list>
#include<map>
#include<set>
#include<sstream>
#include<stack>
#include<queue>
#include<string>
#include<bitset>
#include<algorithm>
#pragma warning(disable:4996)
#define me(s)  memset(s,0,sizeof(s))
#define _for(i,a,b) for(int i=(a);i<(b);++i)
#define _rep(i,a,b) for(int i=(a);i<=(b);++i)
#define Max(a,b) (a)>(b)?(a):(b);
#define Min(a,b) (a)<(b)?(a):(b);
using namespace std;
typedef pair <int, int> pii;
typedef long long ll;
typedef unsigned long long llu;
const int INT_INF = 0x3f3f3f3f;
const int INT_M_INF = 0x7f7f7f7f;
const ll LL_INF = 0x3f3f3f3f3f3f3f3f;
const ll LL_M_INF = 0x7f7f7f7f7f7f7f7f;
const int dr[] = { 0, -1, 0, 1, -1, -1, 1, 1 };
const int dc[] = { -1, 0, 1, 0, -1, 1, -1, 1 };
const int MOD = 1e9 + 7;
const double pi = acos(-1.0);
const double eps = 1e-15;
const int maxn = 11;
int n, m;
int g[maxn][maxn];
int vis[4][maxn * 2];
int maxd;
bool judge()
{
	_for(i, 0, n)
		_for(j, 0, m)
		if (g[i][j] && !vis[0][i] && !vis[1][j] && !vis[2][i + j] && !vis[3][i - j + maxn]) return false;
	return true;
}
int dfs(int i, int j, int dep)
{
	if (dep == maxd) {
		if (judge()) return true;
		return false;
	}
	while (i < n) {
		while (j<m) {
			int t1 = vis[0][i], t2 = vis[1][j], t3 = vis[2][i + j], t4 = vis[3][i - j + maxn];
			vis[0][i] = vis[1][j] = vis[2][i + j] = vis[3][i - j + maxn] = 1;
			if (dfs(i, j + 1, dep + 1)) return true;
			vis[0][i] = t1; vis[1][j] = t2; vis[2][i + j] = t3; vis[3][i - j + maxn] = t4;
			++j;
		}
		j %= m; ++i;
	}	
	return false;
}
int main()
{
	int kcase = 0;
	while (scanf("%d", &n) == 1 && n) {
		scanf("%d", &m);
		me(g);
		_for(i, 0, n) {
			getchar();
			_for(j, 0, m) {
				if (getchar() == 'X') g[i][j] = 1;
			}
		}
		printf("Case %d: ", ++kcase);
		for (maxd = 0; maxd < 5; maxd++) {
			me(vis);
			if (dfs(0, 0, 0)) break;
		}
		printf("%d\n", maxd);
	}
}