TYVJ2477 架设电话线

#include<iostream>
#include<cstdio>
#include<cstring>
#include<string>
#include<algorithm>
#include<vector>
#include<queue>
using namespace std;
const int maxn = 20005,maxint = 0x3fffffff;
struct edge{
    int v;
    int w;
};
int n,p,k,dis[maxn],mx;
bool inq[maxn];
vector<edge> g[maxn];
void input(){
    cin>>n>>p>>k;
    int u,v,w;
    edge tmp;
    mx = 0;
    for(int i = 1;i <= p;i++){
        scanf("%d%d%d",&u,&v,&w);
        tmp.v = v;
        tmp.w = w;
        g[u].push_back(tmp);
        tmp.v = u;
        g[v].push_back(tmp);
        mx = max(mx,w);
    }
}
void spfa(int t){
    memset(inq,false,sizeof(inq));
    for(int i = 1;i <= n;i++) dis[i] = maxint;
    queue<int> q;
    inq[1] = true;
    dis[1] = 0;
    q.push(1);
    while(!q.empty()){
        int u = q.front(),v,w;
        inq[u] = false;
        q.pop();
        for(int i = 0;i < g[u].size();i++){
            v = g[u][i].v;
            w = g[u][i].w > t ? 1 : 0;
            if(dis[u] + w < dis[v]){
                dis[v] = dis[u] + w;
                if(!inq[v]){
                    inq[v] = true;
                    q.push(v);
                }
            }
        }
    }
}
bool check(int t){
    spfa(t);
    if(dis[n] <= k){
        return true;
    }
    else return false;
}
void div(){
    int lans = 0,rans = mx,mans;
    while(lans <= rans){
        mans = (lans + rans) >> 1;
        if(check(mans)){
            rans = mans - 1;
        }else{
            lans = mans + 1;
        }
    }
    if(check(mans)){
        if(mans > mx) cout<<-1;
        else cout<<mans;
    }else{
        if(mans + 1> mx) cout<<-1;
        else cout<<mans + 1;
    }

}
int main(){
    input();
    div();
    return 0;
}