Submission #1265120

#	Time	Username	Problem	Language	Result	Execution time	Memory
1265120		thaibeo123	Race (IOI11_race)	C++17	100 / 100	635 ms	57788 KiB

race

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

#define ll long long
#define fi first
#define se second
#define pb push_back

const int N = 1e6 + 5;

int n, k, ans = 1e9;
bool centroid[N];
int sz[N];
set<pair<int, int>> s;
vector<pair<int, int>> g[N];

int dfs(int u, int par, int h) {
    sz[u] = 1;
    for (auto b : g[u]) {
        int v = b.fi;
        if (v != par && !centroid[v]) {
            sz[u] += dfs(v, u, h + 1);
        }
    }
    return sz[u];
}

int find_centroid(int u, int par, int n) {
    for (auto b : g[u]) {
        int v = b.fi;
        if (v != par && !centroid[v] && sz[v] > n / 2) {
            return find_centroid(v, u, n);
        }
    }
    return u;
}

void count_path(int u, int par, int h, int e) {
    auto it = s.lower_bound({k - h, 0});
    int cur = 0;
    if (it == s.end()) {
        cur = 1e9;
    }
    else {
        auto siu = *it;
        if (siu.fi != k - h) {
            cur = 1e9;
        }
        else {
            cur = siu.se;
        }
    }
    if (h <= k) {
        ans = min(ans, e + cur);
    }
    for (auto b : g[u]) {
        int v = b.fi, w = b.se;
        if (v != par && !centroid[v] && h + w <= k) {
            count_path(v, u, h + w, e + 1);
        }
    }
}

void update(int u, int par, int h, int e) {
    if (h <= k) {
        s.insert({h, e});
    }
    for (auto b : g[u]) {
        int v = b.fi, w = b.se;
        if (v != par && !centroid[v] && h + w <= k) {
            update(v, u, h + w, e + 1);
        }
    }
}

void solve_centroid(int u) {
    int n = dfs(u, 0, 0);
    int c = find_centroid(u, 0, n);

    centroid[c] = 1;
    s.insert({0, 0});
    for (auto b : g[c]) {
        int v = b.fi;
        int w = b.se;
        if (!centroid[v] && w <= k) {
            count_path(v, c, w, 1);
            update(v, c, w, 1);
        }
    }
    s.clear();
    for (auto b : g[c]) {
        int v = b.fi;
        if (!centroid[v]) {
            solve_centroid(v);
        }
    }
}

int best_path(int a, int b, int H[][2], int L[]) {
    n = a, k = b;
    for (int i = 0; i < n - 1; ++i) {
        int u = H[i][0] + 1;
        int v = H[i][1] + 1;
        int w = L[i];
        g[u].pb({v, w});
        g[v].pb({u, w});
    }
    solve_centroid(1);
    if (ans == 1e9) return -1;
    return ans;
}

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