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;
}