UVa:11624 Fire!

来源：互联网发布：网络淘宝涮单是真的嘛编辑：程序博客网时间：2024/05/14 09:03
多源bfs。注意J一开始就在边界的特殊情况。
#include <iostream>#include <cstdio>#include <cstring>#include <queue>#include <vector>#include <algorithm>#define ll long long#define INF 200000000#define MOD 1000007#define MAXN 4000*1005using namespace std;char grid[1005][1005];int dist[1005][1005];int M[4][2]= {{1,0},{-1,0},{0,1},{0,-1}};struct Point{    int x,y,time;    Point(int a=0,int b=0,int c=0):x(a),y(b),time(c) {}};Point st;int R,C;bool Range(int x,int y){    if(x<1||y<1||x>R||y>C) return false;    return true;}bool Safe(int x,int y){    if(x==1||x==R||y==1||y==C) return true;    return false;}void bfs_fire(int x,int y){    queue<Point> que;    que.push(Point(x,y,0));    dist[x][y]=0;    while(!que.empty())    {        Point p=que.front();        que.pop();        for(int i=0; i<4; ++i)        {            int nx=p.x+M[i][0],ny=p.y+M[i][1],t=p.time+1;            if(!Range(nx,ny)||grid[nx][ny]=='#') continue;            if(dist[nx][ny]<=t) continue;            dist[nx][ny]=t;            que.push(Point(nx,ny,t));        }    }}bool vis[1005][1005];int bfs_J(int x,int y){    if(Safe(x,y)) return 0;    queue<Point> que;    que.push(Point(x,y,0));    memset(vis,0,sizeof(vis));    vis[x][y]=true;    while(!que.empty())    {        Point p=que.front();        que.pop();        for(int i=0; i<4; ++i)        {            int nx=p.x+M[i][0],ny=p.y+M[i][1],t=p.time+1;            if(vis[nx][ny]||!Range(nx,ny)||grid[nx][ny]=='#'||t>=dist[nx][ny]) continue;            vis[nx][ny]=true;            if(Safe(nx,ny)) return t;            que.push(Point(nx,ny,t));        }    }    return -1;}int main(){    int T;    scanf("%d",&T);    while(T--)    {        scanf("%d%d",&R,&C);        for(int i=1; i<=R; ++i)            scanf("%s",grid[i]+1);        memset(dist,0x7f,sizeof(dist));        for(int i=1; i<=R; ++i)            for(int j=1; j<=C; ++j)            {                if(grid[i][j]=='F') bfs_fire(i,j);                else if(grid[i][j]=='J')                {                    st.x=i;                    st.y=j;                }            }        int ans=bfs_J(st.x,st.y);        if(ans==-1) puts("IMPOSSIBLE");        else printf("%d\n",ans+1);    }    return 0;}
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