hdu 1242 Rescue (bfs+优先队列)

题目链接;
http://acm.hdu.edu.cn/showproblem.php?pid=1242

解析：
我是反着做，多个朋友找天使，就是用优先队列按步数排序BFS
而更简单的办法是一个天使找朋友DFS，这样其实就是最简单的dfs
BFS:

#include<cstdio>#include<iostream>#include<cstring>#include<queue>using namespace std;#define MAXN 300#define inf 999999999typedef struct local{    int x,y;    int time;    friend bool operator <(local n1,local n2)    {        return n1.time>n2.time;    }}loca;loca direction[4]={{1,0},{0,1},{-1,0},{0,-1}};char map[MAXN][MAXN];int visit[MAXN][MAXN];loca start[MAXN];int n,m,ans,num;int check(int x,int y){    if(map[x][y]!='#'&&visit[x][y]==0&&x>=1&&x<=n&&y>=1&&y<=m)        return 1;    else        return 0;}void BFS(){    priority_queue<loca>step;    int i;    loca oth;    for(i=0;i<num;i++)    {        visit[start[i].x][start[i].y]=1;        step.push(start[i]);    }    while(step.size())    {        oth=step.top();        if(map[oth.x][oth.y]=='a'&&ans>oth.time)        {            ans=oth.time;            break;        }        step.pop();        int x,y;        loca tmp;        for(i=0;i<4;i++)        {            x=oth.x+direction[i].x;            y=oth.y+direction[i].y;            if(check(x,y))                        {                if(map[x][y]=='x')                {                        tmp.x=x;                        tmp.y=y;                        tmp.time=oth.time+2;                        visit[tmp.x][tmp.y]=1;                        step.push(tmp);                }                else                {                        tmp.x=x;                        tmp.y=y;                        tmp.time=oth.time+1;                        visit[tmp.x][tmp.y]=1;                        step.push(tmp);                }            }        }    }}int main(){    int i,j,s1,s2;    while(scanf("%d%d",&n,&m)!=EOF)    {        num=0;        for(i=1;i<=n;i++)        {            for(j=1;j<=m;j++)            {                cin>>map[i][j];                if(map[i][j]=='r')   //注意有多个起点                {                    start[num].x=i;                    start[num].y=j;                    start[num].time=0;                    num++;                }            }        }        memset(visit,0,sizeof(visit));        ans=inf;        BFS();        if(ans!=inf) printf("%d\n",ans);        else printf("Poor ANGEL has to stay in the prison all his life.\n");    }    return 0;}

DFS:

#include <cstdio>#include <cstdlib>#include <cstring>#include <cmath>#include <climits>const int MAX = 202;char map[MAX][MAX];int visit[MAX][MAX];int n,m,ax,ay,minx;void dfs(int x,int y,int len){    if(x<0 || y<0 || x>=n || y>=m)return;    if(len>=minx)return;    if(map[x][y]=='#')return;    if(visit[x][y]==1)return;    if(map[x][y]=='r'){        if(len<minx)minx=len;        return;    }    if(map[x][y]=='x'){        ++len;    }    visit[x][y]=1;    dfs(x+1,y,len+1);    dfs(x-1,y,len+1);    dfs(x,y+1,len+1);    dfs(x,y-1,len+1);    visit[x][y]=0;}int main(){    //freopen("in.txt","r",stdin);    int i,j,len;    while(scanf("%d %d%*c",&n,&m)!=EOF){        for(i=0;i<n;++i){            for(j=0;j<m;++j){                map[i][j]=getchar();                if(map[i][j]=='a'){                    ax = i;                    ay = j;                }            }            getchar();        }        len = 0;        minx = INT_MAX;        dfs(ax,ay,len);        if(minx!=INT_MAX){            printf("%d\n",minx);        }else{            printf("Poor ANGEL has to stay in the prison all his life.\n");        }    }    return 0;}