POJ - 3662 Telephone Lines

/*********************************************************
*            ------------------                          *
*   author AbyssalFish                                   *
**********************************************************/
#include<cstdio>
#include<iostream>
#include<string>
#include<cstring>
#include<queue>
#include<vector>
#include<stack>
#include<vector>
#include<map>
#include<set>
#include<algorithm>
#include<cmath>
#include<numeric>
using namespace std;

int N, P, K;
const int MAX_P = 2e4, MAX_N = 1e3+1;

int hd[MAX_N], nx[MAX_P], le[MAX_P], to[MAX_P], ec;
#define eachedge int i = hd[u]; ~i; i = nx[i]
void add(int u,int v,int l)
{
    le[ec] = l;
    to[ec] = v;
    nx[ec] = hd[u];
    hd[u] = ec++;
}

int d[MAX_N];

typedef pair<int,int> pii;
#define dst first
#define nd second
priority_queue<pii,vector<pii>,greater<pii> > q;
const int INF = 0x3f3f3f3f;
bool dijkstra(int mx)
{
    memset(d+1,0x3f,sizeof(int)*N);
    q.push(pii(d[N] = 0,N));
    while(q.size()){
        pii x = q.top(); q.pop();
        if(x.dst != d[x.nd]) continue;
        int u = x.nd;
        for(eachedge){
            int v = to[i], l = (le[i]<=mx?0:1);
            if(d[v] > d[u]+l){
                q.push(pii(d[v] = d[u]+l,v));
            }
        }
    }
    return d[1]<=K;
}



int solve()
{
    if(dijkstra(0)) return 0;
    if(d[1] >= INF) return -1;

    int lb = 1e6, ub = 0, md;
    for(int i = 0; i < ec; i += 2) {
        lb = min(lb,le[i]);
        ub = max(ub,le[i]);
    }

    while(lb < ub){
        md = (lb+ub)>>1;
        dijkstra(md) ? ub = md: lb = md+1;
    }
    return lb;
}

//#define LOCAL
int main()
{
#ifdef LOCAL
    freopen("in.txt","r",stdin);
#endif
    scanf("%d%d%d",&N,&P,&K);
    memset(hd,-1,sizeof(hd));
    for(int i = 0; i < P; i++){
        int a,b,l;
        scanf("%d%d%d",&a,&b,&l);
        add(a,b,l);
        add(b,a,l);
    }
    printf("%d\n",solve());
    return 0;
}