[bzoj2763][JLOI2011]飞行路线——分层图最短路

水题。不多说什么。

#include <bits/stdc++.h>
using namespace std;
const int maxn = 10010;
const int maxk = 15;
int n, m, k, s, t;
struct edge {
  int to, value;
};
struct state {
  int pos;
  int k;
};
vector<edge> G[maxn];
int dist[maxn][maxk], inq[maxn][maxk];
void add_edge(int u, int v, int w) {
  G[u].push_back((edge){v, w});
  G[v].push_back((edge){u, w});
}
void spfa() {
  memset(dist, 0x3f, sizeof(dist));
  dist[s][0] = 0;
  queue<state> q;
  q.push((state){s, 0});
  memset(inq, 0, sizeof(inq));
  inq[s][0] = 1;
  while (!q.empty()) {
    state u = q.front();
    q.pop();
    inq[u.pos][u.k] = 0;
    for (int i = 0; i < G[u.pos].size(); i++) {
      edge &e = G[u.pos][i];
      if (dist[e.to][u.k] > dist[u.pos][u.k] + e.value) {
        dist[e.to][u.k] = dist[u.pos][u.k] + e.value;
        if (!inq[e.to][u.k]) {
          q.push((state){e.to, u.k});
          inq[e.to][u.k] = 1;
        }
      }
      if (u.k < k && dist[e.to][u.k + 1] > dist[u.pos][u.k]) {
        dist[e.to][u.k + 1] = dist[u.pos][u.k];
        if (!inq[e.to][u.k + 1]) {
          q.push((state){e.to, u.k + 1});
          inq[e.to][u.k + 1] = 1;
        }
      }
    }
  }
}
int main() {
  // freopen("input", "r", stdin);
  scanf("%d %d %d", &n, &m, &k);
  scanf("%d %d", &s, &t);
  while (m--) {
    int a, b, c;
    scanf("%d %d %d", &a, &b, &c);
    add_edge(a, b, c);
  }
  spfa();
  int ans = 0x3f3f3f;
  for (int i = 0; i <= k; i++)
    ans = min(ans, dist[t][i]);
  printf("%d\n", ans);
  return 0;
}