杭电 1072 Nightmare

题目传送门

　　　　　　　　　　　　　　Nightmare

　　　　　　　Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 65536/32768 K (Java/Others)
　　　　　　　　　　　　　Total Submission(s): 15242 Accepted Submission(s): 7413
　　　　　　　　　　　　　
Problem Description

Ignatius had a nightmare last night. He found himself in a labyrinth with a time bomb on him. The labyrinth has an exit, Ignatius should get out of the labyrinth before the bomb explodes. The initial exploding time of the bomb is set to 6 minutes. To prevent the bomb from exploding by shake, Ignatius had to move slowly, that is to move from one area to the nearest area(that is, if Ignatius stands on (x,y) now, he could only on (x+1,y), (x-1,y), (x,y+1), or (x,y-1) in the next minute) takes him 1 minute. Some area in the labyrinth contains a Bomb-Reset-Equipment. They could reset the exploding time to 6 minutes.

Given the layout of the labyrinth and Ignatius’ start position, please tell Ignatius whether he could get out of the labyrinth, if he could, output the minimum time that he has to use to find the exit of the labyrinth, else output -1.

Here are some rules:

1. We can assume the labyrinth is a 2 array.
2. Each minute, Ignatius could only get to one of the nearest area, and he should not walk out of the border, of course he could not walk on a wall, too.
3. If Ignatius get to the exit when the exploding time turns to 0, he can’t get out of the labyrinth.
4. If Ignatius get to the area which contains Bomb-Rest-Equipment when the exploding time turns to 0, he can’t use the equipment to reset the bomb.
5. A Bomb-Reset-Equipment can be used as many times as you wish, if it is needed, Ignatius can get to any areas in the labyrinth as many times as you wish.
6. The time to reset the exploding time can be ignore, in other words, if Ignatius get to an area which contain Bomb-Rest-Equipment, and the exploding time is larger than 0, the exploding time would be reset to 6.

Input

The input contains several test cases. The first line of the input is a single integer T which is the number of test cases. T test cases follow.
Each test case starts with two integers N and M(1<=N,Mm=8) which indicate the size of the labyrinth. Then N lines follow, each line contains M integers. The array indicates the layout of the labyrinth.
There are five integers which indicate the different type of area in the labyrinth:
0: The area is a wall, Ignatius should not walk on it.
1: The area contains nothing, Ignatius can walk on it.
2: Ignatius’ start position, Ignatius starts his escape from this position.
3: The exit of the labyrinth, Ignatius’ target position.
4: The area contains a Bomb-Reset-Equipment, Ignatius can delay the exploding time by walking to these areas.

Output

For each test case, if Ignatius can get out of the labyrinth, you should output the minimum time he needs, else you should just output -1.

Sample Input

3
3 3
2 1 1
1 1 0
1 1 3
4 8
2 1 1 0 1 1 1 0
1 0 4 1 1 0 4 1
1 0 0 0 0 0 0 1
1 1 1 4 1 1 1 3
5 8
1 2 1 1 1 1 1 4 
1 0 0 0 1 0 0 1 
1 4 1 0 1 1 0 1 
1 0 0 0 0 3 0 1 
1 1 4 1 1 1 1 1

Sample Output

4
-1
13

解题思路

　　简单的 BFS 问题。有些朋友会纠结其中的回路问题，其实完全不用刻意管它…如果非要管的话，可以定义一个二维数组，来记录已经走过的点的所剩时间，当再次经过此点时，就比较现剩时间和上次走所剩时间，如果现剩时间不大于上次走所剩的时间，说明这个点没有入队的必要。这样就可以解决回路的困扰了。

参考代码

#include<iostream>
#include<cstdio>
#include<queue>
using namespace std;
int n,m,a[10][10];
int d[][2]={1,0 ,-1,0 ,0,1 ,0,-1};
struct lei
{
    int x,y;        //坐标
	int time;       //剩余时间
	int step;       //到此点走了多少步
}st,ed;
int BFS()
{
    queue<lei> q;
    lei k,c;
    c.x=st.x; c.y=st.y; 
	c.step=0; c.time=6;
	k.time=6;
    q.push(c);
    while(!q.empty())
    {
        c=q.front();
        q.pop();
        for(int i=0;i<4;i++)         //四个方向
        {
            k.x=c.x+d[i][0];
            k.y=c.y+d[i][1];
            k.time=c.time-1;
            k.step=c.step+1;
            if(k.time>0&&a[k.x][k.y]&&k.x>0&&k.x<=n&&k.y>0&&k.y<=m)
            {
                if(k.x==ed.x&&k.y==ed.y )
                {
                    return k.step;
                }
                if(a[k.x][k.y]==4)
                {
                    k.time=6;
                    a[k.x][k.y]=0;
                }
                q.push(k);
            }
        }
    }
    return -1;
}
int main()
{
    int T;
    scanf("%d",&T);
    while(T--)
    {
        scanf("%d %d",&n,&m);
        for(int i=1;i<=n;i++)
		{
            for(int j=1;j<=m;j++)
            {
                scanf("%d",&a[i][j]);
                if(a[i][j]==2)
                {
                    st.x=i; st.y=j;
                }
                if(a[i][j]==3)
                {
                    ed.x=i; ed.y=j;
                }
            }
		}
        printf("%d\n",BFS());
    }
    return 0;
}