hdu1242(bfs+優先隊列)

題目鏈接：題目鏈接

題意：X代表衛兵，a代表終點，r代表起始點，.代表路，#代表牆
     路花費一秒，x花費兩秒
     問到達終點的最少時間

思路：bfs 優先隊列存儲走的步數  

c++代碼

#include <stdio.h>
#include <string.h>
#include <queue>
using namespace std;

struct node
{
    int x,y,step;
    friend bool operator<(node n1,node n2)
    {
        return n2.step<n1.step;
    }
};

int n,m,vis[205][205];
char map[205][205];
int x1,x2,y1,y2;
int to[4][2] = {1,0,-1,0,0,1,0,-1};

int check(int x,int y)
{
    if(x<0 || y<0 || x>=n || y>=m || !vis[x][y] || map[x][y] == '#')
        return 1;
    return 0;
}

int bfs()
{
    int i;
    priority_queue<node> Q;
    node a,next;
    a.x = x1;
    a.y = y1;
    a.step = 0;
    Q.push(a);
    vis[x1][y1] = 0;
    while(!Q.empty())
    {
        a = Q.top();
        Q.pop();
        if(a.x == x2 && a.y == y2)
            return a.step;
        for(i = 0; i<4; i++)
        {
            next = a;
            next.x+=to[i][0];
            next.y+=to[i][1];
            if(check(next.x,next.y))//判斷
                continue;
            next.step++;
            if(map[next.x][next.y] == 'x')//衛兵處多花費了一秒
                next.step++;
            if(vis[next.x][next.y]>=next.step)//存入最小時間
            {
                vis[next.x][next.y] = next.step;
                Q.push(next);
            }
        }
    }
    return 0;
}

int main()
{
    int i,j;
    while(~scanf("%d%d",&n,&m))
    {
        for(i = 0; i<n; i++)
        {
            scanf("%s",map[i]);
            for(j = 0; map[i][j]; j++)
            {
                if(map[i][j] == 'r')
                {
                    x1 = i;
                    y1 = j;
                }
                else if(map[i][j] == 'a')
                {
                    x2 = i;
                    y2 = j;
                }
            }
        }
        memset(vis,1,sizeof(vis));
        int ans = 0;
        ans = bfs();
        if(ans)
            printf("%d\n",ans);
        else
            printf("Poor ANGEL has to stay in the prison all his life.\n");
    }

    return 0;
}