Submission #998190

#	Time	Username	Problem	Language	Result	Execution time	Memory
998190		The_Samurai	Race (IOI11_race)	C++17	100 / 100	244 ms	63316 KiB

race

#include "bits/stdc++.h"
#include "race.h"
using namespace std;
using ll = long long;
const int inf = 1e9, N = 2e5 + 5;
int ans = inf, k, z = 0;

vector<vector<pair<int, int>>> g(N);
vector<int> par(N, -1), heavy(N), height2(N);
vector<ll> height(N);
vector<set<pair<ll, int>>> st;

/*
*/

int dfs(int u) {
    int size = 1, max_child_size = 0;
    for (auto [v, w]: g[u]) {
        if (par[u] == v) continue;
        height[v] = height[u] + w;
        height2[v] = height2[u] + 1;
        par[v] = u;
        int child_size = dfs(v);
        if (child_size > max_child_size) {
            heavy[u] = heavy[v];
            max_child_size = child_size;
        }
        size += child_size;
    }
    if (size == 1) {
        heavy[u] = z++;
        st.emplace_back();
    }
    return size;
}

void dfs2(int u) {
    for (auto [v, w]: g[u]) {
        if (par[u] == v) continue;
        dfs2(v);
    }
    for (auto [v, w]: g[u]) {
        if (par[u] == v or heavy[u] == heavy[v]) continue;
        for (auto it: st[heavy[v]]) {
            ll need = k - (it.first - height[u]) + height[u];
            auto it2 = st[heavy[u]].lower_bound(make_pair(need, 0));
            if (it2 != st[heavy[u]].end() and it2->first == need) {
                ans = min(ans, it.second + it2->second - 2 * height2[u]);
            }
        }
        for (auto it: st[heavy[v]]) {
            st[heavy[u]].insert(it);
        }
        st[heavy[v]].clear();
    }
    ll need = k + height[u];
    auto it = st[heavy[u]].lower_bound(make_pair(need, 0));
    if (it != st[heavy[u]].end() and it->first == need) {
        ans = min(ans, it->second - height2[u]);
    }
    st[heavy[u]].emplace(height[u], height2[u]);
    // vector<pair<ll, int>> del;
    // pair<ll, int> last = {-1, -1};
    // for (auto it: st[heavy[u]]) {
    //     if (it.first == last.first) {
    //         del.emplace_back(it);
    //     }
    //     last = it;
    // }
    // for (auto it: del) st[heavy[u]].erase(it);
}

int best_path(int n, int K, int H[][2], int L[]) {
    k = K;
    for (int i = 0; i < n - 1; i++) {
        g[H[i][0]].emplace_back(H[i][1], L[i]);
        g[H[i][1]].emplace_back(H[i][0], L[i]);
    }
    // change it
    dfs(0);
    dfs2(0);
    return ans == inf ? -1 : ans;
}

• Subtask 1: 9 / 9
• Subtask 2: 12 / 12
• Subtask 3: 22 / 22
• Subtask 4: 57 / 57