POJ 3662 Telephone Lines(二分+最短路)

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　　最小化第K大值。　　　　

　　让我怀疑人生的一题目，我有这么笨？

#include <cstdio>
#include <queue>
#include <cstring>
#include <vector>
#include <functional>
using namespace std;
#define maxv 1010
#define maxl 1000000
struct edge
{
    int to, cost;
    edge(){}
    edge(int to, int cost) : to(to), cost(cost){}
};
typedef pair<int, int> P;
vector<edge> G[maxv];
int d[maxv];
int V, E;
int dij(int s, int x) {
    priority_queue<P, vector<P>, greater<P> > que;
    memset(d, 0X3f, V*sizeof(int));
    d[s] = 0;
    que.push(P(0, s));
    while (!que.empty()) {
       P p = que.top(); que.pop();
        int v = p.second;
        if (d[v] < p.first) continue;
        for (int i = 0; i < G[v].size(); ++i)
        {
            edge e = G[v][i];
            int new_d = d[v] + (e.cost >= x ? 1 : 0);
            if (d[e.to] > new_d)
            {
                d[e.to] = new_d;
                que.push(P(d[e.to], e.to));
            }
        }        
    }
    return d[V-1];
}
int main(void) {
    freopen("in.txt", "r", stdin);
    freopen("out.txt", "w", stdout);
    int K;
    scanf("%d%d%d", &V, &E, &K); 
    for (int i = 0; i < E; ++i) {
        int A, B, L;
        scanf("%d%d%d", &A, &B, &L);
        --A, --B;
        G[A].push_back(edge(B,L));
        G[B].push_back(edge(A,L));
    }
    int l = 0, u = maxl+9;
    for (;(u-l) > 1;) {
        int m = (u+l) >> 1;
        if (dij(0, m) > K) {
            l = m;
        } else {
            u = m;
        }
    }
    printf("%d
", (l>maxl ? -1 : l));
    return 0;
}