[Swust OJ 1023]--Escape(带点其他状态的BFS)

 

解题思路：http://acm.swust.edu.cn/problem/1023/

Time limit(ms): 5000　　　　　　　　Memory limit(kb): 65535

 

 

Description

BH is in a maze,the maze is a matrix,he wants to escape!

 

Input

The input consists of multiple test cases.

For each case,the first line contains 2 integers N,M( 1 <= N, M <= 100 ).

Each of the following N lines contain M characters. Each character means a cell of the map.

Here is the definition for chracter.

For a character in the map: 

'S':BH's start place,only one in the map.

'E':the goal cell,only one in the map.

'.':empty cell.

'#':obstacle cell.

'A':accelerated rune.

BH can move to 4 directions(up,down,left,right) in each step.It cost 2 seconds without accelerated rune.When he get accelerated rune,moving one step only cost 1 second.The buff lasts 5 seconds,and the time doesn't stack when you get another accelerated rune.(that means in anytime BH gets an accelerated rune,the buff time become 5 seconds).

 

 

Output

The minimum time BH get to the goal cell,if he can't,print "Please help BH!".

 

Sample Input

5 5

....E

.....

.....

##...

S#...

 

5 8

........

........

..A....A

A######.

S......E

Sample Output

Please help BH!

12

 

由于OJ上传数据的BUG,换行请使用"\r\n"，非常抱歉

 

题目大意：一个迷宫逃离问题，只是有了加速符A,正常情况下通过一个格子2s,有了加速符只要1s,并且加速符持续5s,‘S'代表起点

　　　　　'E'代表终点，'#'代表障碍，'.'空格子，能够逃离输出最少用时，否则输出"Please help BH!"

解题思路：BFS，用一个3维dp数组存贮，每一点在不同加速状态下的值，然后筛选dp数组终点的最小值即可

代码如下：

#include <iostream>
#include <cstring>
#include <queue>
#include <algorithm>
using namespace std;

#define maxn 101
#define inf 0x3f3f3f3f

int dir[][2] = { 1, 0, 0, 1, -1, 0, 0, -1 };
int dp[maxn][maxn][6];
int sx, sy, ex, ey, n, m;
char map[maxn][maxn];

struct node{
    int x, y, step, speed;//spead加速
};
void bfs(){
    node now, next;
    now.x = sx, now.y = sy, now.step = 0, now.speed = 0;
    dp[sx][sy][0] = 0;
    queue<node>Q;
    Q.push(now);
    while (!Q.empty()){
        now = Q.front(); Q.pop();
        for (int i = 0; i < 4; i++){
            next = now;
            next.x += dir[i][0];
            next.y += dir[i][1];
            if (next.x < 0 || next.x >= n || next.y < 0 || next.y >= m || map[next.x][next.y] == '#')continue;//不可行状态
            if (next.speed){
                //加速效果
                next.speed--;
                next.step++;
            }
            else next.step += 2;
            if (map[next.x][next.y] == 'A')next.speed = 5;//获得加速神符
            if (next.step < dp[next.x][next.y][next.speed]){
                dp[next.x][next.y][next.speed] = next.step;
                Q.push(next);
            }
        }
    }
    int ans = inf;
    for (int i = 4; i >= 0; i--)
        ans = min(ans, dp[ex][ey][i]);
    if (ans >= inf)
        cout << "Please help BH!\r\n";
    else
        cout << ans << "\r\n";
}
int main(){
    while (cin >> n >> m){
        memset(dp, inf, sizeof dp);
        for (int i = 0; i < n; i++){
            cin >> map[i];
            for (int j = 0; j < m; j++){
                if (map[i][j] == 'S')sx = i, sy = j;
                if (map[i][j] == 'E')ex = i, ey = j;
            }
        }
        bfs();
    }
    return 0;
}