Robot Motion HDU1035（dfs+模拟）

                                             

   A robot has been programmed to follow the instructions in its path. Instructions for the next direction the robot is to move are laid down in a grid. The possible instructions are 

N north (up the page)
S south (down the page)
E east (to the right on the page)
W west (to the left on the page)

For example, suppose the robot starts on the north (top) side of Grid 1 and starts south (down). The path the robot follows is shown. The robot goes through 10 instructions in the grid before leaving the grid.

Compare what happens in Grid 2: the robot goes through 3 instructions only once, and then starts a loop through 8 instructions, and never exits.

You are to write a program that determines how long it takes a robot to get out of the grid or how the robot loops around.   

 关于这个题，主要运用dfs模拟这个过程。在写这道题时遇到很多错误，主要就是根据题意模拟这个过程。

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
char s[1005][1005];
int vis[1005][1005],m,n,k,flag;
void dfs(int a,int b){
	int step=1;           // step记录走的步数
	while(1){                  // 模拟这个过程
		if(a == m || a < 0 || b < 0 || b == n){              // 超过这个矩阵时退出
			printf("%d step(s) to exit\n",step-1); 
			return;
		}
		if(vis[a][b]){                                   // 标记，如果这个点走过时，就会退出
			printf("%d step(s) before a loop of %d step(s)\n",vis[a][b]-1,step-vis[a][b]);
			return;
		}
		vis[a][b] = step;
		if(s[a][b] == 'N') a--;
		else if(s[a][b] == 'S') a++;
		else if(s[a][b] == 'E') b++;
		else if(s[a][b] == 'W') b--;
		step++;
	}
}
int  main(){
	while(cin >> m>>n>>k&&n&&m){
		memset(vis,0,sizeof(vis));
		for(int i = 0;i < m ;i++)
			scanf("%s",s[i]);
		k--;                           // 因为是从0，开始的，所以就减去1
		dfs(0,k);
	}
	return 0;
}