hdu 1242 Rescue(A*索搜)

http://acm.hdu.edu.cn/showproblem.php?pid=1242
题意是从r找到a，路过.时间+1,路过x时间+2，#围墙，求最短的时间。
用a[n][m]保存位置，围墙为-1，.为1，x为2。用A*索搜计算出每一步的f值，在通过优先队列f最小的开始出队列，直到找到为止。

s为当前已用的时间。
h为预测到目标地点的时间下界。
f=s+h；

代码：

#include<iostream>
#include<queue>
using namespace std;
int _move[4][2] = { { 1, 0 }, { -1, 0 }, { 0, 1 }, { 0, -1 }};
int b;
struct node
{
    int f, s, h;
    int x, y, step;
    friend bool operator<(node n1, node n2)
    {
        return n2.f<n1.f;
    }
};
int n, m,a[205][205];
int s_x, s_y, e_x, e_y;
int getH(int x,int y){
    return abs(x - e_x) + abs(y - e_y);
}
int isOk(int x, int y){
    if (x < 0 || x >= n || y < 0 || y >= m) return 0;
    return 1;
}
void bfs(){
    priority_queue<node> qu;
    node now,temp;
    now.x = s_x;     now.y = s_y;
    now.h = getH(s_x, s_y); now.s = 0;
    now.f = now.h + now.s;
    qu.push(now);
    while (qu.size()>0)
    {
        now = qu.top(); qu.pop();
        if (now.x == e_x&&now.y == e_y){
            cout << now.s<<endl;
            b = 1;
            return;
        }
        a[now.x][now.y] = -1;
        for (int i = 0; i < 4; i++){
            temp.x = now.x + _move[i][0];
            temp.y = now.y + _move[i][1];
            if (isOk(temp.x, temp.y) && a[temp.x][temp.y] >= 0){
                temp.s = now.s + a[temp.x][temp.y];
                temp.h = getH(temp.x,temp.y);
                temp.f = temp.s + temp.h;
                qu.push(temp);
            }
        }
    }

}
int main(){
    while (cin>>n>>m)
    {
        b = 0;
        char temp;
        for (int i = 0; i < n; i++){
            for (int j = 0; j < m; j++){
                cin >> temp;
                if (temp == '.') a[i][j] = 1;
                else if (temp == 'x') a[i][j] = 2;
                else if (temp == 'r'){
                    a[i][j] = 1;
                    e_x = i;
                    e_y = j;
                }
                else if (temp == 'a'){
                    a[i][j] = 0;
                    s_x = i;
                    s_y = j;

                }
                else
                {
                    a[i][j] = -1;
                }
            }
        }
        bfs();
        if (!b) cout << "Poor ANGEL has to stay in the prison all his life." << endl;
    }
}