BFS HDOJ 1242 Rescue

 

题目传送门

题意：从r走到a，遇到x多走一步，问最小走到a的步数

分析：因为r有多个，反过来想从a走到某个r的最小步数，简单的BFS。我对这题有特殊的感情，去年刚来集训队时肉鸽推荐了这题，当时什么都不会，看个数组模拟队列的BFS看的头晕，现在看起来也不过如此，额，当年开始是从r走到a的，因为数据巨弱才过的，应该要用到优先队列。

/************************************************
* Author        :Running_Time
* Created Time  :2015/9/25 星期五 09:13:51
* File Name     :B_BFS.cpp************************************************/#include <cstdio>
#include <algorithm>
#include <iostream>
#include <sstream>
#include <cstring>
#include <cmath>
#include <string>
#include <vector>
#include <queue>
#include <deque>
#include <stack>
#include <list>
#include <map>
#include <set>
#include <bitset>
#include <cstdlib>
#include <ctime>
using namespace std;#define lson l, mid, rt << 1
#define rson mid + 1, r, rt << 1 | 1
typedef long long ll;
const int N = 2e2 + 10;
const int INF = 0x3f3f3f3f;
const int MOD = 1e9 + 7;
const double EPS = 1e-8;
struct Angle    {int x, y, step;Angle () {}Angle (int x, int y, int step) : x (x), y (y), step (step) {}
};
int dx[4] = {-1, 1, 0, 0};
int dy[4] = {0, 0, -1, 1};
bool vis[N][N];
char maze[N][N];
int n, m;bool judge(int x, int y)    {if (x < 1 || x > n || y < 1 || y > m || vis[x][y] || maze[x][y] == '#') return false;else    return true;
}void BFS(Angle s)    {int ret = INF;memset (vis, false, sizeof (vis));queue<Angle> Q; Q.push (s);vis[s.x][s.y] = true;while (!Q.empty ()) {Angle r = Q.front ();   Q.pop ();for (int i=0; i<4; ++i) {int tx = r.x + dx[i];int ty = r.y + dy[i];if (!judge (tx, ty))  continue;vis[tx][ty] = true;if (maze[tx][ty] == 'r')    {ret = min (ret, r.step + 1);    continue;}else if (maze[tx][ty] == 'x')   {Q.push (Angle (tx, ty, r.step + 2));    continue;}else    Q.push (Angle (tx, ty, r.step + 1));}}if (ret == INF) puts ("Poor ANGEL has to stay in the prison all his life.");else    printf ("%d\n", ret);
}int main(void)   {while (scanf ("%d%d", &n, &m) == 2) {for (int i=1; i<=n; ++i)    {scanf ("%s", maze[i] + 1);}bool find = false;  Angle start;for (int i=1; i<=n && !find; ++i)    {for (int j=1; j<=m; ++j)    {if (maze[i][j] == 'a')  {start = Angle (i, j, 0);find = true;    break;}}}BFS (start);}return 0;
}

 

当年的代码不忍直视。。。

#include<stdio.h>
typedef struct point
{int x,y,step;
}target;
int N,M,dir[4][2]={0,1,0,-1,1,0,-1,0},ax,ay;
int flag[202][202];
char map[302][302];
target que[40005];
int BFS(target start)
{int end,top,i;int min=1000000;target in,next;end=top=0;que[top]=start;while (top>=end){in=que[end];end=(end+1);for (i=0;i<4;i++){next.x=in.x+dir[i][0];next.y=in.y+dir[i][1];if (map[next.x][next.y]=='r'){if (min>in.step+1)min=in.step+1;}if (next.x>=0&&next.x<N&&next.y>=0&&next.y<M&&map[next.x][next.y]!='#'){if (flag[next.x][next.y]>in.step+1){next.step=in.step+1;if (map[next.x][next.y]=='x')next.step++;flag[next.x][next.y]=next.step;top=(top+1);que[top]=next;}}}}if (min!=1000000)return min;elsereturn -1;
}
int main()
{int i,j,num;target start;while (scanf("%d%d",&N,&M)!=EOF){for (i=0;i<N;i++){scanf("%s",map[i]);for (j=0;j<M;j++){flag[i][j]=1000000;if (map[i][j]=='a'){//map[i][j]='.';ax=i;ay=j;}}}start.x=ax;start.y=ay;start.step=0;//map[ax][ay]='.';num=BFS(start);if (num==-1)printf("Poor ANGEL has to stay in the prison all his life.\n");elseprintf("%d\n",num);}return 0;
}