广搜之解救行动

用优先级队列来存放准备扩展的结点，时间少的在队首

#include <iostream>
#include <memory.h>
#include <string>
#include <stdio.h>
#include <queue>
#include <math.h>
#include <stdlib.h>
using namespace std;
int N,M,T,BeginX,BeginY,EndX,EndY;
char Map[205][205];
int dx[] = {1,-1,0,0};
int dy[] = {0,0,1,-1};
int visited[205][205];
struct node
{
    int x,y,step;
    node(int xx=0,int yy=0,int ss=0):x(xx),y(yy),step(ss) {}
    friend bool operator <(const node &a, const node &b)
    {
        return a.step > b.step;
    }
};
priority_queue <node> q;
void Bfs()
{
    q.push( node( BeginX, BeginY, 0) );
    visited[BeginX][BeginY] = 1;
    while( !q.empty() )
    {
        node now = q.top();
        q.pop();
        int NowX = now.x;
        int NowY = now.y;
        int NowStep = now.step;
        if( NowX == EndX && NowY == EndY )
        {
            cout << NowStep << endl;
            return;
        }
        for( int i = 0; i < 4; i++ )
        {
            int NextX = NowX + dx[i];
            int NextY = NowY + dy[i];
            if( !visited[NextX][NextY] && Map[NextX][NextY] != '#' )
            {
                if( Map[NextX][NextY] == '@' || Map[NextX][NextY] == 'a' )
                {
                    q.push( node( NextX, NextY, NowStep + 1));
                    visited[NextX][NextY] = 1;
                }
                else if( Map[NextX][NextY] == 'x' )
                {
                    q.push( node( NextX, NextY, NowStep + 2));
                    visited[NextX][NextY] = 1;
                }
            }
        }
    }
    cout << "Impossible" << endl;
}
int main()
{
    cin >> T;
    while( T-- )
    {
        cin >> N >> M;
        memset(Map, 0, sizeof(Map));
        memset(visited, 0, sizeof(visited));
        for( int i = 1; i <= N; i++ )
            for( int j = 1; j <= M; j++ )
            {
                cin >> Map[i][j];
                if( Map[i][j] == 'r' )
                {
                    BeginX = i;
                    BeginY = j;
                }
                if( Map[i][j] == 'a' )
                {
                    EndX = i;
                    EndY = j;
                }
            }
        for( int i = 0; i <= N+1; i++ )
            for( int j = 0; j <= M+1; j++ )
                if( i==0 || j==0 || i==N+1 || j==M+1 )
                    Map[i][j] = '#';
        while( !q.empty() )
            q.pop();
        Bfs();
    }
    return 0;
}