杭电OJ 1175（C++）

#include <iostream>
#include <cstring>
using namespace std;
const int MAXN = 1005;

int maze[MAXN][MAXN]; //迷宫数组
bool vis[MAXN][MAXN]; //访问数组
bool flag; //是否能消除
int n, m, q; //输入
int sx, sy, ex, ey; //起点，终点
int dicx[4] = { 1,-1,0,0 }; //x轴移动方向
int dicy[4] = { 0,0,1,-1 }; //y轴移动方向

//深搜，x，y为当前坐标，dic为当前方向，turns为当前转弯次数
void dfs(int x, int y, int dic, int turns)
{
	//转弯次数大于2或者已经找到，停止
	if (turns > 2 || flag)
		return;
	//转弯次数为2，且目前与目标不在同一直线上，剪枝
	if (turns == 2 && (x - ex) != 0 && (y - ey) != 0)
		return;
	if (x == ex && y == ey && turns <= 2) //到达目标，搜索成功 
	{
		flag = 1;
		return;
	}
	for (int i = 0; i < 4; ++i) //搜索四个方向 
	{
		int nx = x + dicx[i]; //下一步的x坐标
		int ny = y + dicy[i]; //下一步的y坐标
		if (nx < 1 || nx > n || ny < 1 || ny > m || vis[nx][ny]) //边界和访问情况
			continue;
		if (maze[nx][ny] == 0 || (nx == ex && ny == ey))
		{
			vis[nx][ny] = 1;
			if (dic == -1 || dic == i) //目前是第一步或者前进方向没有变化
				dfs(nx, ny, i, turns);
			else //前进方向变化
				dfs(nx, ny, i, turns + 1);
			vis[nx][ny] = 0; //回溯
		}
	}
	return;
}

int main()
{
	while (cin >> n >> m)
	{
		if (n == 0 && m == 0)
			break;
		memset(maze, 0, sizeof(maze));

		for (int i = 1; i <= n; ++i)
		{
			for (int j = 1; j <= m; ++j)
				cin >> maze[i][j];
		}
		cin >> q;
		for (int i = 0; i < q; ++i)
		{
			cin >> sx >> sy >> ex >> ey;
			memset(vis, 0, sizeof(vis));
			flag = 0;
			if (maze[sx][sy] == maze[ex][ey] && maze[sx][sy] != 0)
				dfs(sx, sy, -1, 0); //将初始方向设为-1 

			if (flag)
				cout << "YES" << endl;
			else
				cout << "NO" << endl;
		}
	}
	return 0;
}