Submission #1117444

#	Time	Username	Problem	Language	Result	Execution time	Memory
1117444		vjudge1	Race (IOI11_race)	C++17	100 / 100	630 ms	42232 KiB

race

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

#define ll long long int

const int N = 2e5 + 1;
int n, k, max_depth;
int sz[N];
bool vis[N];
vector<pair<int, int>> adj[N];
int res = INT_MAX;
map<int, int> cnt;

int get_subtree_size(int u, int p)
{
    sz[u] = 1;
    for (auto [v, w] : adj[u])
    {
        if (v != p and !vis[v])
            sz[u] += get_subtree_size(v, u);
    }
    return sz[u];
}
int get_centroid(int u, int p, int tree_size)
{
    for (auto [v, w] : adj[u])
    {
        if (v != p and !vis[v] and (sz[v] * 2 > tree_size))
            return get_centroid(v, u, tree_size);
    }
    return u;
}
void calc(int u, int p, int fill, int weight, int depth = 1)
{
    if (fill == 1)
    {
        if (cnt.count(weight))
        {
            cnt[weight] = min(cnt[weight], depth);
        }
        else
        {
            cnt[weight] = depth;
        }
    }
    else if ((weight <= k) and (cnt.count(k - weight)))
    {
        res = min(res, depth + cnt[k - weight]);
    }
    for (auto [v, w] : adj[u])
    {
        if (!vis[v] and (v != p))
            calc(v, u, fill, weight + w, depth + 1);
    }
}

void decompose(int u, int p)
{
    int tree_size = get_subtree_size(u, p);
    int centroid = get_centroid(u, p, tree_size);
    vis[centroid] = true;
    cnt.clear();
    cnt[0] = 0;
    for (auto [v, w] : adj[centroid])
    {
        if (!vis[v] and v != p)
            calc(v, centroid, 0, w), calc(v, centroid, 1, w);
    }
    for (auto [v, w] : adj[centroid])
    {
        if (!vis[v] and v != p)
            decompose(v, centroid);
    }
}

int best_path(int N, int K, int edges[][2], int weight[2])
{
    n = N;
    k = K;
    for (int i = 0; i < n - 1; ++i)
    {
        int u, v, w;
        u = edges[i][0];
        v = edges[i][1];
        w = weight[i];
        adj[u].push_back({v, w});
        adj[v].push_back({u, w});
    }
    decompose(0, -1);
    if (res == INT_MAX)
        return -1;
    return res;
}

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