P1948 [USACO08JAN]电话线Telephone Lines

#include<bits/stdc++.h>
using namespace std;
const int bow=1010;
const int INF=0x3f3f3f3f;
int n,m,k,a,b,c,ne,head[bow],dis[1001],vist[1001];
struct node{int nxt,to,dis;}eg[100100];
void adde(int u,int v,int val){eg[++ne].nxt=head[u];eg[ne].to=v;eg[ne].dis=val;head[u]=ne;}
int check(int w){
    queue<int>q;
    for(int i=1;i<=n;i++)dis[i]=INF; 
    q.push(1);dis[1]=0;vist[1]=1;
    while(!q.empty()){
    int u=q.front();
    q.pop();vist[u]=0;
    for(int i=head[u];i;i=eg[i].nxt)
    {
        int l=0;
        if(eg[i].dis>w)l=1;
        if(dis[eg[i].to]>dis[u]+l){
            dis[eg[i].to]=dis[u]+l;
            if(!vist[eg[i].to]){vist[eg[i].to]=1;q.push(eg[i].to);}
        }  
    }
    }
    if(dis[n]>k)return 0;
    else return 1;
}
int main()
{
    cin>>n>>m>>k;
    while(m--)
    {
        cin>>a>>b>>c;
        adde(a,b,c);
        adde(b,a,c);
    }
    int l=0,r=1000005,ans=INF;
    while(l<=r)
    {
        int mid=(l+r)/2;
        if(check(mid)){ans=mid,r=mid-1;}
        else l=mid+1;
    }
    if(ans>=1000005)ans=-1;
    cout<<ans;
}