Submission #826114

#	Time	Username	Problem	Language	Result	Execution time	Memory
826114		SoulKnight	Race (IOI11_race)	C++17	100 / 100	2422 ms	53964 KiB

race

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

#define ll long long
#define ln '\n'

const int N = 2e5 + 5;
const int LG = 20;
const int INF = 0x3f3f3f3f;
const int MOD = 998244353;


int n, k;
int h[N][2], l[N];

int sz[N], ans = INF;
vector<pair<int, int>> adj[N];
bitset<N> removed;

map<ll, int> mn;


void init(){
    cin >> n >> k;
    for (int i = 0; i < n-1; i++) cin >> h[i][0] >> h[i][1] >> l[i];
}

int get_size(int u, int p){
    sz[u] = 1;
    for (auto& [v, e]: adj[u]){
        if (v == p || removed[v]) continue;
        sz[u] += get_size(v, u);
    }
    return sz[u];
}

int get_centroid(int u, int p, int s){
    for (auto& [v, e]: adj[u]){
        if (v == p || removed[v]) continue;
        if (sz[v] > s / 2) return get_centroid(v, u, s);
    }
    return u;
}

void dfs(int u, int p, int dep, int cur_len, int m){
    // cout << u << ' ' << p << ' ' << dep << ' ' << cur_len << ' ' << m << ln;
    if (cur_len > k) return;

    if (mn.find(k-cur_len) == mn.end()) mn[k-cur_len] = INF;
    if (mn.find(cur_len) == mn.end()) mn[cur_len] = INF;

    if (m == 1) {ans = min(ans, dep + mn[k-cur_len]);}
    else mn[cur_len] = min(mn[cur_len], dep);


    for (auto& [v, e]: adj[u]){
        if (v == p || removed[v]) continue;
        dfs(v, u, dep+1, cur_len + e, m);
    }
}

void build(int u){
    int c = get_centroid(u, -1, get_size(u, -1));
    // cout << "centroid " << c << ln;
    removed[c] = 1;



    for (auto& [v, e]: adj[c]){
        if (removed[v]) continue;
        dfs(v, c, 1, e, 1);
        dfs(v, c, 1, e, 0);
    }
    // cout << ans << ln;
    mn.clear();
    mn[0] = 0;

    for (auto& [v, e]: adj[c]){
        if (removed[v]) continue;
        build(v);
    }
}


int solve(){
    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]});
    }

    mn[0] = 0;
    build(1);
    return ((ans == INF)? -1: ans);
}

void init(int N, int K, int H[][2], int L[]){
  n = N;
  k = K;
  for (int i = 0; i < n-1; i++){
    h[i][0] = H[i][0];
    h[i][1] = H[i][1];
    l[i] = L[i];
  }


}


int best_path(int N, int K, int H[][2], int L[])
{
  init(N, K, H, L);
  return solve();
}

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