hdu 1175冒牌连连看

#include <bits/stdc++.h>
using namespace std;
const int N = 1005;
int arr[N][N];
int vis[N][N];
int n, m;
int dx[4] = { 0,1,0,-1 };
int dy[4] = { 1,0,-1,0 };
bool flag;
int si, sj, ei, ej;
bool ok(int nx, int ny) {
	if (nx<=0 || ny<=0 || nx>n || ny>m)return false;
	return true;
}
int cnt = 0;
void dfs(int x, int y,int lastdir,int k) {
	if (flag==true)return;
	if (k > 3)return;
	if (k == 3 && x - ei != 0 && y - ej != 0)return;
	for (int i = 0;i < 4;i++) {
		int nx = x + dx[i];
		int ny = y + dy[i];
		if (vis[nx][ny])continue;
		if (ok(nx,ny)) {	
			if (nx == ei&&ny == ej && (k <= 2 || k == 3 && i == lastdir)) {
				flag = true;
				return;
			}
			if (arr[nx][ny] != 0)continue;
			vis[nx][ny] = 1;
			if (k==0||i != lastdir)
				dfs(nx, ny, i, k+1);
			else
				dfs(nx, ny, i, k);
			vis[nx][ny] = 0;
		}
	}
}
int main() {
	while (~scanf("%d%d", &n, &m)) {
		if (n == 0 && m == 0)break;
		for (int i = 1;i <= n;i++) {
			for (int j = 1;j <= m;j++) {
				scanf("%d", &arr[i][j]);
			}
		}
		int t;
		scanf("%d", &t);
		while (t--) {
			flag = false;
			scanf("%d%d%d%d", &si, &sj, &ei, &ej);
			if (arr[si][sj] != 0 && arr[ei][ej] != 0) {
				if (arr[si][sj] == arr[ei][ej]) {
					if (!(si == ei&&sj == ej)) {
						vis[si][sj] = 1;
						dfs(si, sj, 0, 0);
						vis[si][sj] = 0;
					}
				}
			}
			if (flag)printf("YES
");
			else printf("NO
");
		}
	}
	return 0;
}