Submission #836285

#	Time	Username	Problem	Language	Result	Execution time	Memory
836285		lamduybao03	Valley (BOI19_valley)	C++14	100 / 100	440 ms	69144 KiB

valley

#include <bits/stdc++.h>
#define int long long
#define sqr(x) ((x) * (x))
using namespace std;
typedef pair<int, int> pi;
typedef pair<pi, int> ppi;
const int mod = 1e9+7;
const int inv_2 = (mod+1) / 2;


int32_t main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    #ifdef LOCAL
        freopen("input.txt", "r", stdin);
        //freopen("output.txt", "w", stdout);
    #endif
    int n, s, q, e;
    cin >> n >> s >> q >> e;
    map<pi, int> edge_to_id;
    vector<vector<pi>> adj(n+1);
    for(int i = 1; i < n; i++) {
        int u, v, w;
        cin >> u >> v >> w;
        adj[u].push_back({v, w});
        adj[v].push_back({u, w});
        edge_to_id[{u, v}] = i;
        edge_to_id[{v, u}] = i;
    }
    vector<int> par(n+1);
    vector<int> d(n+1);
    vector<int> h(n+1);
    vector<int> vis(n+1);
    vector<int> pos(n+1);
    vector<int> down(n+1, 1e18);
    for(int i = 0; i < s; i++) {
        int u;
        cin >> u;
        down[u] = 0;
    }
    function<void(int)> dfs = [&] (int u) {
        vis[u] = 1;
        for(auto p : adj[u]) {
            int v = p.first;
            int w = p.second;
            if(!vis[v]) {
                pos[edge_to_id[{u, v}]] = v;
                par[v] = u;
                d[v] = d[u] + w;
                h[v] = h[u] + 1;
                dfs(v);
                down[u] = min(down[u], down[v] + w);
            }
        }
    };
    dfs(e);
    for(int i = 1; i <= n; i++)
        down[i] = down[i] - d[i];
    vector<vector<int>> p(20, vector<int> (n+1));
    vector<vector<int>> dis(20, vector<int> (n+1, 1e18));
    for(int i = 1; i <= n; i++) {
        p[0][i] = par[i];
        dis[0][i] = down[i];
    }
    for(int i = 1; i < 20; i++) {
        for(int j = 1; j <= n; j++) {
            p[i][j] = p[i-1][p[i-1][j]];
            dis[i][j] = min(dis[i-1][j], dis[i-1][p[i-1][j]]);
        }
    }
    function<int(int, int)> lca = [&] (int u, int v) {
        if(h[u] < h[v]) {
            swap(u, v);
        }
        int delta = h[u] - h[v];
        for(int i = 0; i < 20; i++) {
            if(delta & (1 << i)) {
                u = p[i][u];
            }
        }
        if(u == v)
            return u;
        for(int i = 19; i >= 0; i--) {
            if(p[i][u] != p[i][v]) {
                u = p[i][u];
                v = p[i][v];
            }
        }
        u = p[0][u];
        v = p[0][v];
        if(u != v)
            throw 0;
        return u;
    };
    function<int(int, int)> get = [&] (int u, int k) {
        int s = 1e18;
        for(int i = 0; i < 20; i++) {
            if(k & (1 << i)) {
                s = min(s, dis[i][u]);
                u = p[i][u];
            }
        }
        return s;
    };
    while(q--) {
        int i, u;
        cin >> i >> u;
        int v = pos[i];
        if(lca(u, v) != v) {
            cout << "escaped\n";
        }
        else {
            int delta = h[u] - h[v] + 1;
            int s = get(u, delta) + d[u];
            if(s > 1e17)
                cout << "oo\n";
            else
                cout << s << "\n";
        }
    }
}

• Subtask 1: 9 / 9
• Subtask 2: 27 / 27
• Subtask 3: 23 / 23
• Subtask 4: 41 / 41