Uva 10816 Travel in Desert 【SPFA+二分】

http://acm.hust.edu.cn:8080/judge/problem/viewProblem.action?id=19157

關鍵：將溫度進行二分，每個二分溫度進行SPFA求出最短路

#include<iostream>#include<vector>#include<map>#include<stack>#include<algorithm>#include<queue>#include<list>#include<set>#include<string.h>#include<stdlib.h>#include<math.h>#include<stdio.h>#include<ctype.h>#include<iomanip>using namespace std;#define LL long long#define pi acos(-1)#define N 1010#define INF 999999999double dis[N];int pre[N];int vis[N];int s,t;int n,m;struct node{    int next;    double w,l;};vector<node> v[N];void init(){    int i;    for(i=1;i<=n;i++)        v[i].clear();}double spfa(double k){    int i,j;    queue<int> q;    for(i=1;i<=n;i++)    dis[i]=INF;    dis[s]=0;    memset(vis,0,sizeof(vis));    vis[s]=1;    while(!q.empty())q.pop();    q.push(s);    while(!q.empty())    {        int temp=q.front();        q.pop();        vis[temp]=0;        for(i=0;i<(int)v[temp].size();i++)        {            int to=v[temp][i].next;            if(dis[to]>dis[temp]+v[temp][i].l && v[temp][i].w<=k)                {                    dis[to]=dis[temp]+v[temp][i].l;                    if(!vis[to])                    {                        vis[to]=1;                        q.push(to);                    }                        pre[to]=temp;                }        }    }    return dis[t];}void print(int x){    if(x==s)    {        printf("%d ",s);        return ;    }    print(pre[x]);    if(x==t)        printf("%d\n",t);    else    printf("%d ",x);}int main(){//    freopen("a.txt","r",stdin);    int i,j,k;    while(scanf("%d%d",&n,&m)!=EOF)    {        scanf("%d%d",&s,&t);        init();        int a,b;        double w,l;        node p;        double le=INF,r=0,mid;        for(i=0;i<m;i++)        {            scanf("%d%d%lf%lf",&a,&b,&w,&l);            p.next=b, p.w=w, p.l=l;            v[a].push_back(p);            p.next=a;            v[b].push_back(p);            if(w<le)le=w;            if(w>r)r=w;        }         while(fabs(r-le)>1e-8)        {            mid=(le+r)/2;          //cout<<le<<" "<<mid<<" "<<r<<endl;            double len=spfa(mid);            if(len!=INF)            r=mid;            else            le=mid;        }        double ans=spfa(r);        print(t);        printf("%.1f %.1f\n",ans,r);    }    return 0;}