Submission #805304

#	Time	Username	Problem	Language	Result	Execution time	Memory
805304		Kerim	Race (IOI11_race)	C++17	100 / 100	347 ms	122516 KiB

race

#include "race.h"
#include "bits/stdc++.h"
#define ll long long

using namespace std;

typedef pair<int, int> pii;
const int N = 2e5+5;
const int INF = 1e9;
vector<pii> adj[N];
int K, answer;
int dp[N][105];

void dfs(int nd, int pr){
    dp[nd][0] = 0;
    for (int i = 1; i <= K; i++)
        dp[nd][i] = INF;
    for (auto [c, e]: adj[nd]){
        if (c == pr)
            continue;
        dfs(c, nd);
        //update answer
        for (int w1 = 0; w1 + e <= K; w1++){
            int w2 = K - e - w1;
            answer = min(answer, dp[nd][w1] + dp[c][w2]+1);
        }
        //update dp
        for (int p = 0; p+e <= K; p++)
            dp[nd][p+e] = min(dp[nd][p+e],dp[c][p]+1);
    }
}

void dfs1(int nd, int pr, int lvl, ll weight){
    if (weight == K)
        answer = min(answer, lvl);
    if (weight >= K)
        return;
    for (auto [c, e]: adj[nd]){
        if (c == pr)
            continue;
        dfs1(c, nd, lvl+1, weight+e);
    }
}

map<ll, int> m[N];
void dfs2(int nd, int pr, ll W, int L){
    m[nd].clear();
    m[nd][W] = L;
    for (auto [c, e]: adj[nd]){
        if (c == pr)
            continue;
        dfs2(c, nd, W+e, L+1);
        if (m[nd].size() < m[c].size())
            swap(m[nd], m[c]);
        //update answer
        for (auto [w1, l1]: m[c]){
            int w2 = K - w1 + 2*W;
            if (m[nd].find(w2) != m[nd].end()){
                int l2 = m[nd][w2];
                answer = min(answer, l1 + l2 - 2*L); 
            }
        }
        //update map
        for (auto [w1, l1]: m[c]){
            if (m[nd].find(w1) == m[nd].end())
                m[nd][w1] = l1;
            else
                m[nd][w1] = min(m[nd][w1], l1);
        }
        m[c].clear();
    }
}
int best_path(int n, int k, int H[][2], int L[]){
    K = k;
    answer = INF;
    for (int i = 0; i < n - 1; i++){
        int u = H[i][0], v = H[i][1], w = L[i];
        adj[u].push_back({v, w});
        adj[v].push_back({u, w});
    }
    if (k <= 100) //subtask 1 and 3
        dfs(1, -1);
    else if(n <= 1000){ //subtask 2
        for (int i = 0; i < n; i++)
            dfs1(i, -1, 0, 0);
    }
    else{
        dfs2(1, -1, 0, 0);
    }
    if (answer == INF)
        answer = -1;
    return answer;
}

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