poj 2449 k短路模板（有环）

#include <iostream>
#include <cstdio>
#include <cstring>
#include <vector>
#include <queue>

using namespace std;

const int maxn = 1000 + 10;
const int INF = 1<<29;

vector<int>E[maxn], W[maxn], Ek[maxn], Wk[maxn];
int d[maxn];
bool vis[maxn];

struct Node {
    int u, len;
    Node(int tu, int tlen) : u(tu), len(tlen) {}
    Node(){}
    bool operator < (const Node & rhs) const {
        return len + d[u] > rhs.len + d[rhs.u];
    }
};


int k_road(int s, int t, int n, int k) {
    priority_queue<Node>q;
    q.push(Node(s, 0));
    int tk = 0;
    while(!q.empty()) {
        Node f = q.top(); q.pop();
        if(f.u == t) {
            tk++;
            if(tk == k) {
                return f.len;
            }
        }
        int u = f.u;
        for( int i=0; i<Ek[u].size(); i++ ) {
            int v = Ek[u][i];
            q.push(Node(v, f.len+Wk[u][i]));
        }
    }
    return -1;
}

void spfa(int s, int t, int n) {
    for( int i=1; i<=n; i++ ) d[i] = INF;
    d[t] = 0;
    queue<int>q;
    q.push(t);
    memset(vis, 0, sizeof(vis));
    vis[t] = true;
    while(!q.empty()) {
        int f = q.front(); q.pop(); vis[f] = false;
        for( int i=0; i<E[f].size(); i++ ) {
            int v = E[f][i];
            if(d[v] > d[f] + W[f][i]) {
                d[v] = d[f] + W[f][i];
                if(vis[v] == false) {
                    vis[v] = true;
                    q.push(v);
                }
            }
        }
    }
}

int main() {
    //freopen("in","r", stdin);
    int n, m;
    while(scanf("%d%d", &n, &m) != EOF) {
        int s, t, k;
        for( int i=1; i<=n; i++ ) E[i].clear(), W[i].clear(), Ek[i].clear(), Wk[i].clear();
        for( int i=0; i<m; i++ ) {
            int u, v, w;
            scanf("%d%d%d", &v, &u, &w);
            E[u].push_back(v);
            W[u].push_back(w);
            Ek[v].push_back(u);
            Wk[v].push_back(w);
        }
        scanf("%d%d%d", &s, &t, &k);
        if(s == t) k++;
        spfa(s, t, n);
        if(d[s] == INF) {
            printf("-1\n");
            continue;
        }
        /*for( int i=1; i<=n; i++ ) printf("%d ", d[i]);
        printf("\n");*/
        int ans = k_road(s, t, n, k);
        if(ans == -1) printf("-1\n");
        else printf("%d\n", ans);
    }
    return 0;
}