Contest1882 - 2019秋个人训练赛2（补题场）

#include <bits/stdc++.h>
 
using namespace std;
const int maxn=21000;
struct node
{
    int v,nxt,w;
} e[maxn];
int n,k,t,head[maxn],vis[maxn],d[maxn],m;
 
void add(int u,int v,int w)
{
    t++;
    e[t].v=v;
    e[t].w=w;
    e[t].nxt=head[u];
    head[u]=t;
}
 
bool check(int mid)
{
    memset(vis,0,sizeof(vis));
    memset(d,0x3f,sizeof(d));
    d[1]=0;
    priority_queue<pair<int,int>,vector<pair<int,int> >,greater<pair<int,int> > >q;
    q.push(make_pair(d[1],1));
    while (!q.empty())
    {
        int u=q.top().second;
        q.pop();
        vis[u]=1;
        for (int i=head[u]; i; i=e[i].nxt)
        {
            int v=e[i].v,w=d[u];
            if (vis[v])
                continue;
            if (e[i].w>=mid)
                w++;
            if (d[v]>w)
            {
                d[v]=w;
                q.push(make_pair(d[v],v));
            }
        }
    }
    return d[n]>=k+1;
}
 
int main()
{
    scanf("%d%d%d",&n,&m,&k);
    for (int i=1,u,v,w; i<=m; i++)
    {
        scanf("%d%d%d",&u,&v,&w);
        add(u,v,w);
        add(v,u,w);
    }
    int l=0,r=1e6+100,ans=-1;
    while (l<=r)
    {
        int mid=(l+r)>>1;
        if (check(mid))
        {
            l=mid+1;
            ans=mid;
        }
        else
            r=mid-1;
    }
    if (ans>1e6)
        printf("-1\n");
    else if (r<0)
        printf("0\n");
    else
        printf("%d",ans);
    return 0;
}