poj 3037 Skiing

来源：互联网发布：如何评价苏联知乎编辑：程序博客网时间：2024/05/17 22:18

//每个点的速度固定，与路径无关，SPFA

#include<iostream>
#include<cstdio>
#include<cstring>
#include<queue>
#include<cmath>
using namespace std;
const double inf=1e200;
const int maxn=10005;
double p2[105];
int h[105][105], n, pre[maxn], inqueue[maxn], cnt, v, r, c;
double ans, d[maxn];
struct node{
    int v, w, next;
}edge[maxn*4];
void add_edge(int s, int e, int w){
    edge[cnt].v=e;
    edge[cnt].w=w;
    edge[cnt].next=pre[s];
    pre[s]=cnt++;
}
void init(){
    int i, j, x, y;
    p2[50]=1;
    for(i=1; i<=50; i++){
        p2[50-i]=p2[51-i]/2;
        p2[50+i]=p2[49+i]*2;
    }
    memset(pre, -1, sizeof(pre));
    cnt=0;
    scanf("%d%d%d", &v, &r, &c);
    n=r*c;
    for(i=1; i<=r; i++)
    for(j=1; j<=c; j++)
    scanf("%d", &h[i][j]);
    for(i=1; i<=r; i++)
    for(j=1; j<=c; j++){
        x=(i-1)*c+j;
        if(i<r){
            y=i*c+j;
            add_edge(x, y, h[i][j]);
        }
        if(i>1){
            y=(i-2)*c+j;
            add_edge(x, y, h[i][j]);
        }
        if(j>1){
            y=(i-1)*c+j-1;
            add_edge(x, y, h[i][j]);
        }
        if(j<c){
            y=(i-1)*c+j+1;
            add_edge(x, y, h[i][j]);
        }
    }
}

bool spfa(int st){
    int i, s, head;
    for(i=1; i<=n; i++){
        d[i]=inf;
        inqueue[i]=0;
    }
    d[st]=0;
    inqueue[st]=1;
    queue<int >q;
    q.push(st);
    while(!q.empty()){
        head=q.front();
        q.pop();
        inqueue[head]=0;
        s=pre[head];
        while(s!=-1){
            if(d[edge[s].v]>d[head]+1.0/(p2[h[1][1]-edge[s].w+50]*v)){
                d[edge[s].v]=d[head]+1.0/(p2[h[1][1]-edge[s].w+50]*v);
                if(!inqueue[edge[s].v]){
                    inqueue[edge[s].v]=1;
                    q.push(edge[s].v);
                }
            }
            s=edge[s].next;
        }
    }
    return true;
}
int main(){
    //freopen("1.txt", "r", stdin);
    init();
    spfa(1);
    printf("%.2f\n", d[n]);
    return 0;
}