HDU 1242 Rescue (DFS+剪枝，一个起点多个终点)

Discription

题意：天使被困在监狱，他的朋友们想见他，监狱的地形复杂，包括路(用点标示),墙(用#标示)，天使的位置（用a标示），他的朋友(用r标示),监狱里还有守卫(用x标示),他的朋友只能向左右上下四个方向走，走以不花一单位时间，若碰上守卫，消灭守卫需要额外花费一单位时间。问最少多长时间天使能见到他的朋友。

Sample Input

7 8

#.#####.#.a#..r.#..#x.....#..#.##...##...#..............

Sample Output

13

Solution

注意不只有一个朋友，所以采用一个起点搜索多个终点，注意中间剪枝，如果采用多个起点搜索一个终点思路会T。

#include <iostream>#include <cstdio>#include <algorithm>#include <vector>#include <cstring>#include <ctime>#include <utility>using namespace std;#define ONLINE_JUDGEchar m[400][400];int visit[400][400];int COUNT, N, M;int xx[4] = {0, 0, -1, 1};int yy[4] = {-1, 1, 0, 0};void init(){    memset(m, 0, sizeof(m));    memset(visit, 0, sizeof(visit));}void dfs(int x, int y, int count){    if (m[x][y] == 'r')    {        COUNT = min(COUNT, count);        return;    }    if (count >= COUNT)        return;    for (int i = 0; i < 4; i++)    {        int nx = x + xx[i];        int ny = y + yy[i];        if (!visit[nx][ny] && nx >= 1 && nx <= N && ny >= 1 && ny <= M && m[nx][ny] != '#')        {            visit[nx][ny] = 1;            if (m[x][y] == 'x')                dfs(nx, ny, count + 2);            else                dfs(nx, ny, count + 1);            visit[nx][ny] = 0;        }    }}int main(){#ifndef ONLINE_JUDGE    freopen("in.txt", "r", stdin);    long _begin_time = clock();#endif    pair<int, int> start;    while (~scanf("%d%d", &N, &M))    {        init();        for (int i = 1; i <= N; i++)        {            for (int j = 1; j <= M; j++)            {                cin >> m[i][j];                if (m[i][j] == 'a')                    start = make_pair(i, j);            }        }        COUNT = 0x3f3f3f3f;        visit[start.first][start.second] = 1;        dfs(start.first, start.second, 0);        if (COUNT < 0x3f3f3f3f)            printf("%d\n", COUNT);        else            printf("Poor ANGEL has to stay in the prison all his life.\n");    }#ifndef ONLINE_JUDGE    long _end_time = clock();    printf("time = %.2f ms\n", double(_end_time - _begin_time) / CLOCKS_PER_SEC * 1000);#endif    return 0;}