Submission #574402

#	Time	Username	Problem	Language	Result	Execution time	Memory
574402		talant117408	Race (IOI11_race)	C++17	100 / 100	2133 ms	48452 KiB

race

#include "race.h"
#include <bits/stdc++.h>

#ifndef EVAL
#include "grader.cpp"
#endif
 
using namespace std;
 
typedef long long ll;
typedef pair <int, int> pii;
typedef pair <ll, ll> pll;
 
#define pb                  push_back
#define mp                  make_pair
#define all(v)              (v).begin(),(v).end()
#define sz(v)               int((v).size())
#define do_not_disturb      ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define endl                '\n'
 
int mod = 1e9+7;
 
ll modulo(ll a) {
    return ((a % mod) + mod) % mod;
}
 
ll add(ll a, ll b) {
    return modulo(a + b);
}
 
ll mult(ll a, ll b) {
    return modulo(a * b);
}
 
ll binpow(ll a, ll b) {
    ll res = 1;
    while (b) {
        if (b&1) {
            res = mult(res, a);
        }
        a = mult(a, a);
        b >>= 1;
    }
    return res;
}

const int MAXN = 2e5+7;
vector <pll> graph[MAXN];
ll ans = 9e18;
multiset <pll> paths;
ll n, KK;
int used[MAXN], subtree[MAXN];

void dfs(int v, int p) {
    subtree[v] = 1;
    for (auto to : graph[v]) {
        if (used[to.first] || to.first == p) continue;
        dfs(to.first, v);
        subtree[v] += subtree[to.first];
    }
}

int find_centroid(int v, int p, int saizu) {
    for (auto to : graph[v]) {
        if (used[to.first] || to.first == p) continue;
        if (subtree[to.first] * 2 > saizu) {
            return find_centroid(to.first, v, saizu);
        }
    }
    return v;
}

void get_paths(int v, int p, ll dist, int len, bool flag) {
    if (flag) {
        paths.insert(mp(dist, len));
    }
    else {
        paths.erase(paths.find(mp(dist, len)));
    }
    for (auto to : graph[v]) {
        if (used[to.first] || to.first == p) continue;
        get_paths(to.first, v, dist+to.second, len+1, flag);
    }
}

void calculate(int v, int p, ll dist, int len) {
    auto it = paths.lower_bound(mp(KK-dist, 0));
    if (it != paths.end() && (*it).first == KK-dist) {
        ans = min(ans, len+(*it).second);
    }
    for (auto to : graph[v]) {
        if (used[to.first] || to.first == p) {
            continue;
        }
        calculate(to.first, v, dist+to.second, len+1);
    }
}

void centroid_decomposition(int v) {
    dfs(v, v);
    auto centroid = find_centroid(v, v, subtree[v]);
    used[centroid] = 1;
    
    get_paths(centroid, centroid, 0, 0, 1);
    for (auto to : graph[centroid]) {
        if (used[to.first]) continue;
        get_paths(to.first, centroid, to.second, 1, 0);
        calculate(to.first, to.first, to.second, 1);
        get_paths(to.first, centroid, to.second, 1, 1);
    }
    get_paths(centroid, centroid, 0, 0, 0);
    
    for (auto to : graph[centroid]) {
        if (!used[to.first]) {
            centroid_decomposition(to.first);
        }
    }
}

int best_path(int N, int k, int h[][2], int l[]) {
    n = N;
    KK = k;
    for (int i = 0; i < n-1; i++) {
        graph[h[i][0]].pb(mp(h[i][1], l[i]));
        graph[h[i][1]].pb(mp(h[i][0], l[i]));
    }
    centroid_decomposition(1);
    return (ans > n ? -1 : ans);
}

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