1240번: 노드사이의 거리 ↗

#include <bits/stdc++.h>

#define for1(s,n) for(int i = s; i < n; i++)
#define for1j(s,n) for(int j = s; j < n; j++)
#define foreach(k) for(auto i : k)
#define foreachj(k) for(auto j : k)
#define pb(a) push_back(a)
#define sz(a) a.size()
#define INF (ll)1e18

using namespace std;

typedef unsigned long long ull;
typedef long long ll;
typedef vector <int> iv1;
typedef vector <vector<int>> iv2;
typedef vector <ll> llv1;
typedef unsigned int uint;
typedef vector <ull> ullv1;
typedef vector <vector <ull>> ullv2;

struct edge {
    ll node;
    ll cost;
    bool operator<(const edge &to) const {
        return cost > to.cost;
    }
};

struct WGraph {
    ll n; 
    vector<vector<edge>> adj;
    vector<ll> prev;
    WGraph(ll n) : n{n}, adj(n+1) {}
    void addEdge(ll s, ll e, ll cost) {
        adj[s].push_back({e, cost});
    }

    void input(ll m) { // 단방향
        ll a, b, c;
        while(m--) {
            cin >> a >> b >> c;
            addEdge(a,b,c);
        }
    }

    void inputD(ll m) { // 양방향
        ll a, b, c;
        while(m--){
            cin >> a >> b >> c;
            addEdge(a,b,c);
            addEdge(b,a,c);
        }
    }

    vector <ll> dijkstra(ll s) {
        vector <ll> dist(n+1, INF);
        prev.resize(n+1, -1);
        priority_queue<edge> pq;
        pq.push({ s, 0ll });
        dist[s] = 0;
        while (!pq.empty()) {
            edge cur = pq.top();
            pq.pop();
            if (cur.cost > dist[cur.node]) continue;
            for (auto &nxt : adj[cur.node])
                if (dist[cur.node] + nxt.cost < dist[nxt.node]) {
                    prev[nxt.node] = cur.node;
                    dist[nxt.node] = dist[cur.node] + nxt.cost;
                    pq.push({ nxt.node, dist[nxt.node] });
                }
        }
        return dist;
    }

    vector<ll> getPath(ll s, ll e) {
        vector<ll> ret;
        ll current = e;
        while(current != -1) {
            ret.push_back(current);
            current = prev[current];
        }
        reverse(ret.begin(), ret.end());
        return ret;
    }
};

ll N, M;

int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    
    cin >> N >> M;
    WGraph w = WGraph(N);
    w.inputD(N-1);

    for1(0, M) {
        ll a, b;
        cin >> a >> b;
        llv1 ret = w.dijkstra(a);
        cout << ret[b] << "\n";
    }
}