算法竞赛模板

2024湖南省赛K

分层dijtra, 如果有多个起点可以开始，一开始把所有的起点放入堆中（相当于一个超级源点），不需要从每个点开始跑。

#include<bits/stdc++.h>
using namespace std;
#define int long long
const int inf = 1e18;
signed main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int n, m;
    cin >> n >> m;
    vector<int> head(n+1), to(2*m+1), nx(2*m+1), v(2*m+1);
    vector<int> c(n+1);
    int id = 1;
    auto ad = [&](int x, int y, int val) {
        v[id] = val; 
        to[id] = y;
        nx[id] = head[x];
        head[x] = id++;
    };
    for (int i = 1; i <= m; i++) {
        int u, v, val;
        cin >> u >> v >> val;
        ad(u,v,val);
        ad(v,u,val);
    }
    vector<vector<int>> dis(n+2,vector<int>(2,inf));
    for (int i = 1; i <= n; i++) {
        cin >> dis[i][0];
    }
    
    struct node {
        int loc;
        int dis;
        bool f;
        bool operator<(node b) const {
            return dis > b.dis;
        }
    };
    priority_queue<node> q;
    vector<vector<bool>> vis(n+2,vector<bool>(2,false));
    for (int i = 1; i <= n; i++) {
        q.push({i,dis[i][0],0});
    }
    
    while(q.size()) {
        node tp = q.top();
        q.pop();
        if (vis[tp.loc][tp.f]) {
            continue;
        }
        vis[tp.loc][tp.f] = true;
        for (int i = head[tp.loc]; i; i = nx[i]) {
            if (tp.f == 0) {
                if (!vis[to[i]][0] && tp.dis + v[i] < dis[to[i]][0]) {
                    dis[to[i]][0] = tp.dis + v[i];
                    q.push({to[i],dis[to[i]][0],0});
                }
                if (!vis[to[i]][1] && tp.dis < dis[to[i]][1]) {
                    dis[to[i]][1] = tp.dis;
                    q.push({to[i],tp.dis,1});
                }
            } else {
                if (!vis[to[i]][1] && tp.dis + v[i] < dis[to[i]][1]) {
                    dis[to[i]][1] = tp.dis + v[i];
                    q.push({to[i],dis[to[i]][1],1});
                }
            }
        }
    }
    int ans = 0;
    for (int i = 1; i <= n; i++) {
        ans = max(ans,min(dis[i][1],dis[i][0]));
    }
    cout << ans << "\n";
    return 0;
}