HDU--2962

原题链接：http://acm.hdu.edu.cn/showproblem.php?pid=2962

分析：最短路+二分。

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<string> 
#include<algorithm>
#include<vector>
#include<queue>
#include<map>
#define ll long long
#define inf 1000000000
#define maxn 1005
using namespace std;
struct edge
{
    int to,h,len;
    edge(int x,int y,int z)
    {
        to=x;h=y;len=z;
    }
};
vector<edge>e[maxn];
queue<int>q;
bool vis[maxn];
int d[maxn],n,m,s,t,H,maxh;
void spfa(const int s,int h)
{
    while(!q.empty())q.pop();
    for(int i=0;i<=n;i++)
    {
        d[i]=inf;vis[i]=false;
    }
    d[s]=0;vis[s]=true;
    q.push(s);
    while(!q.empty())
    {
        int u=q.front();q.pop();
        for(int i=0;i<e[u].size();i++)
        {
            if(e[u][i].h>=h&&d[e[u][i].to]>d[u]+e[u][i].len)
            {
                d[e[u][i].to]=d[u]+e[u][i].len;
                if(!vis[e[u][i].to])
                {
                    vis[e[u][i].to]=true;
                    q.push(e[u][i].to);
                }
            }
        }
        vis[u]=false;
    }
}
int main()
{
    int cas=1;
    while(~scanf("%d%d",&n,&m))
    {
        if(n==0&&m==0)break;
        for(int i=0;i<maxn;i++)e[i].clear();
        int u,v,h,l;
        for(int i=0;i<m;i++)
        {
            scanf("%d%d%d%d",&u,&v,&h,&l);
            if(h==-1)h=inf;
            e[u].push_back(edge(v,h,l));
            e[v].push_back(edge(u,h,l));
        }
        scanf("%d%d%d",&s,&t,&H);
        int lef=1,r=H,maxh=0,ans=inf;
        while(lef<=r)
        {
            int mid=(r+lef)>>1;
            if(mid<=0)break;
            spfa(s,mid);
             if(d[t]!=inf)
            {
                lef=mid+1;
                maxh=mid;
                ans=d[t];
            }
             else r=mid-1;
        }
        if(cas>1)    puts("");
        printf("Case %d:
",cas++);
        if(ans==inf||maxh<1)cout<<"cannot reach destination
";
        else {
              printf("maximum height = %d
",maxh);
                printf("length of shortest route = %d
",ans);
        }
    } 
    return 0;
}