Submission #1151289

#	Time	Username	Problem	Language	Result	Execution time	Memory
1151289		Shadow1	Race (IOI11_race)	C++20	100 / 100	317 ms	81176 KiB

race

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

using ll = long long;

#define pii pair<int,int>
#define fir first
#define sec second
#define sz(x) ll(x.size())
// #define int long long


const int maxn = 2e5 + 5;
map<int, int> mp[maxn];  // mp[u][x] is length of minimum path with u as root and sum = x. (sum, min edges)
vector<pii> adj[maxn], off(maxn);
int n, k, ans = maxn;

void dfs(int u, int p) {
    mp[u][0] = 0;
    for(auto &i : adj[u]) {
        int w = i.sec, v = i.fir;
        if(v == p) continue;
        dfs(v, u);
        off[v].fir += w;
        off[v].sec++;
        // mp[u][w] = 1;
        if(sz(mp[u]) < sz(mp[v])) {
            swap(mp[u], mp[v]);
            swap(off[u], off[v]);
        }
        for(auto &x : mp[v]) {
            int z = k-x.fir-off[v].fir-off[u].fir;
            if(mp[u].count(z)) {
                ans = min(ans, mp[u][z] + x.sec + off[u].sec + off[v].sec);
            }
        }
        for(auto &x : mp[v]) {
            int z = x.fir + off[v].fir - off[u].fir;
            if(mp[u].count(z))
                mp[u][z] = min(mp[u][z], x.sec + off[v].sec - off[u].sec);
            else
                mp[u][z] = x.sec + off[v].sec - off[u].sec;
        }
    }
}

int best_path(int N, int K, int H[][2], int L[])
{
    n = N, k = K;
    for(int i=0; i<n-1; ++i) {
      adj[H[i][0]].push_back({H[i][1], L[i]});
      adj[H[i][1]].push_back({H[i][0], L[i]});
    }
    dfs(0, -1);
    return (ans == maxn ? -1 : ans);
}

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