Submission #1231492

#	Time	Username	Problem	Language	Result	Execution time	Memory
1231492		zut3	Race (IOI11_race)	C++20	100 / 100	343 ms	81284 KiB

race

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

using namespace std;

int n, k;
vector<vector<pair<int, int>>> g;
vector<map<int, int>> d;
vector<int> dist, sum;

int mn = 2e9;
bool have_ans = false;

void dfs(int v, int prev) {
    for(auto [u, w]: g[v]) {
        if(u == prev) continue;

        dist[u] = dist[v]+1;
        sum[u] = sum[v]+w;
        d[u][sum[u]] = dist[u];
        dfs(u, v);
    }
}

void mrg(int v, int prev) {
    int target = k + 2*sum[v];

    for(auto [u, w]: g[v]) {
        if(prev == u) continue;

        mrg(u, v);
        if(d[u].size() > d[v].size()) swap(d[u], d[v]);

        for(auto [key, val]: d[u]) {
            if(d[v].count(target-key)) {
                mn = min(mn, d[v][target-key] + val - 2*dist[v]);
            }
        }
        for(auto [key, val]: d[u]) {
            if(d[v].count(key)) d[v][key] = min(d[v][key], val);
            else d[v][key] = val;
        }
    }
}

int best_path(int N, int K, int H[][2], int L[]) {
    n = N; k = K;

    g.assign(n, vector<pair<int, int>>());
    d.assign(n, map<int, int>());
    dist.assign(n, 0);
    sum.assign(n, 0);

    for(int i = 0; i < n-1; i++) {
        g[H[i][0]].push_back({H[i][1], L[i]});
        g[H[i][1]].push_back({H[i][0], L[i]});
    }

    d[0][0] = 0;

    dfs(0, -1);
    mrg(0, -1);

    if(mn < 1e9) return mn;
    return -1;
}

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