python/TangDou/AcWing/MiniPath/P4568_1.cpp

#include <bits/stdc++.h>
using namespace std;

const int N = 1e4 * 2 * 11 + 10; //节点数：1e4,无向图，1e4*2,共k+1(k<=10)层:1e4*2*11
const int M = 5e4 * 11 * 3 + 10; //边数
typedef pair<int, int> PII;
const int INF = 0x3f3f3f3f;

int dist[N], st[N];

//邻接表
int e[M], h[N], idx, w[M], ne[M];
void add(int a, int b, int c) {
    e[idx] = b, ne[idx] = h[a], w[idx] = c, h[a] = idx++;
}

int n, m, s, t, k;

void dijkstra() {
    priority_queue<PII, vector<PII>, greater<PII>> q;
    dist[s] = 0;
    q.push({0, s});

    while (q.size()) {
        int u = q.top().second;
        q.pop();

        if (st[u]) continue;
        st[u] = true;

        for (int i = h[u]; ~i; i = ne[i]) {
            int j = e[i];
            if (st[j]) continue;
            if (dist[j] > dist[u] + w[i]) {
                dist[j] = dist[u] + w[i];
                q.push({dist[j], j});
            }
        }
    }
}

int main() {
    //多组测试数据
    while (~scanf("%d%d%d", &n, &m, &k)) {
        //初始化
        memset(h, -1, sizeof(h));
        idx = 0;
        memset(dist, 0x3f, sizeof(dist));
        memset(st, false, sizeof(st));

        scanf("%d%d", &s, &t); //起点与终点

        while (m--) {
            int a, b, c;
            scanf("%d%d%d", &a, &b, &c);
            //分层图建图
            for (int i = 0; i <= k; i++) { //创建k+1层分层图
                add(a + i * n, b + i * n, c), add(b + i * n, a + i * n, c); //无向图
                if (i < k)                                                  //从第0层开始，到k-1层结束，都需要向下一层建立通道
                    add(a + i * n, b + (i + 1) * n, 0), add(b + i * n, a + (i + 1) * n, 0);
            }
        }
        //一遍最短路
        dijkstra();

        // k+1个层中，都去找t的最短路径，再取最小值，就是答案
        int ans = INF;
        for (int i = 0; i <= k; i++)
            ans = min(ans, dist[t + i * n]);

        printf("%d\n", ans);
    }
    return 0;
}