Submission #1031669

#	Time	Username	Problem	Language	Result	Execution time	Memory
1031669		TrendBattles	Race (IOI11_race)	C++14	100 / 100	331 ms	38856 KiB

race

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


const int MAX_K = 1 << 20, inf = 0x3f3f3f3f;
int mn[MAX_K];
void minimise(int& x, int y) {
    if (x > y) x = y;
}
int best_path(int N, int K, int H[][2], int L[]) {
    vector <vector <int>> graph(N);
    for (int i = 0; i < N - 1; ++i) {
        graph[H[i][0]].push_back(i);
        graph[H[i][1]].push_back(i);
    }

    vector <int> sub_sz(N), last_v(N, -1), removed(N);
    
    auto Find_Centroid = [&] (int u, int parent, int sz) -> int {
        int last = u;
        while (true) {
            for (int id : graph[u]) {
                int v = H[id][0] ^ H[id][1] ^ u;

                if (v == parent or removed[v]) continue;

                if (sub_sz[v] * 2 > sz) {
                    last = v; break;
                }
            }

            if (last == u) break;
            parent = u; u = last; 
        }
        return last;
    };
    auto get_size = [&] (auto self, int u, int parent) -> int {
        sub_sz[u] = 1;
        for (int id : graph[u]) {
            int v = H[id][0] ^ H[id][1] ^ u;

            if (v == parent or removed[v]) continue;

            sub_sz[u] += self(self, v, u);
        }
        return sub_sz[u];
    };
    vector <int> pending;
    pending.push_back(0);

    memset(mn, 0x3f, sizeof mn);
    int ans = inf;

    vector <int> pref_w(N), depth(N);
    vector <int> cache;

    auto DFS = [&] (auto self, int u, int parent) -> void {
        if (pref_w[u] > K) return;

        minimise(ans, depth[u] + mn[K - pref_w[u]]);

        cache.push_back(u);
        for (int id : graph[u]) {
            int v = H[id][0] ^ H[id][1] ^ u;
            if (v == parent or removed[v]) continue;

            depth[v] = depth[u] + 1;
            pref_w[v] = pref_w[u] + L[id];

            self(self, v, u);
        }
    };
    auto Build_Centroid = [&] (int u, int parent) -> void {
        int cen_node = Find_Centroid(u, parent, get_size(get_size, u, parent));

        int l = 0;
        removed[cen_node] = true;
        depth[cen_node] = 0; pref_w[cen_node] = 0;
        mn[0] = 0;

        for (int id : graph[cen_node]) {
            int v = H[id][0] ^ H[id][1] ^ cen_node;
            if (removed[v]) continue;

            depth[v] = 1;
            pref_w[v] = L[id];

            DFS(DFS, v, cen_node);
            for (; l < (int) cache.size(); l += 1) {
                int& node = cache[l];

                minimise(mn[pref_w[node]], depth[node]);
            }
        }

        for (int x : cache) {
            mn[pref_w[x]] = inf;
        }
        cache.clear();
        
        for (int id : graph[cen_node]) {
            int v = H[id][0] ^ H[id][1] ^ cen_node;
            if (removed[v]) continue;

            last_v[v] = cen_node;
            pending.push_back(v);
        }
    };
    while (not pending.empty()) {
        int u = pending.back(); pending.pop_back();
        Build_Centroid(u, last_v[u]);
    }

    return ans == inf ? -1 : ans;
}

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