Submission #938831

#	Time	Username	Problem	Language	Result	Execution time	Memory
938831		duckindog	Race (IOI11_race)	C++17	43 / 100	225 ms	113924 KiB

race

#pragma GCC optimize("Ofast")
#include <bits/stdc++.h>
 
using namespace std;
 
#ifndef LOCAL
#include "race.h"
#endif
 
const int N = 200'000 + 1;
vector<pair<int, int>> ad[N];
 
namespace sub2 {
  long long d[N], dep[N];
  int f[N][10], st[N], ed[N], it;
  void dfs(int u, int pre = 0) { 
    st[u] = ++it;
    for (int i = 1; i <= 9; ++i)
      f[u][i] = f[f[u][i - 1]][i - 1];
 
    for (const auto& [v, w] : ad[u]) { 
      if (v == pre) continue;
      d[v] = d[u] + w;
      dep[v] = dep[u] + 1;
      f[v][0] = u;
      dfs(v, u);
    }
    ed[u] = it;
  }
  bool anc(int u, int v) { return st[u] <= st[v] && ed[u] >= ed[v]; }
  int lca(int u, int v) { 
    if (anc(u, v)) return u;
    if (anc(v, u)) return v;
 
    for (int i = 9; i >= 0; --i)
      if (!anc(f[u][i], v)) u = f[u][i];
    return f[u][0];
  }
 
  int solve(int n, int k) { 
    dfs(0);
    long long answer = 1e7;
    for (int i = 0; i < n; ++i) { 
      for (int j = i + 1; j < n; ++j) { 
        int l = lca(i, j);
        int distant = d[i] + d[j] - 2 * d[l];
        if (distant == k) answer = min(answer, dep[i] + dep[j] - 2 * dep[l]);
      }
    }
 
    return answer == 1e7 ? -1 : answer; 
  }
 
}
 
namespace sub3 {
  int dpin[N][101];
  int n, k;
  int answer = 1e7;
  void dfs(int u, int pre = 0) { 
    dpin[u][0] = 0;
    for (const auto& [v, w] : ad[u]) { 
      if (v == pre) continue;
      dfs(v, u);
      for (int i = 0; i <= k; ++i) { 
        if (k - i - w < 0) continue;
        answer = min(answer, dpin[v][i] + dpin[u][k - i - w] + 1);
      }
      for (int i = 1; i <= k; ++i) if (i - w >= 0) dpin[u][i] = min(dpin[u][i], dpin[v][i - w] + 1);
    }
  }
  
  int solve(int a, int b) { 
    n = a; k = b;
    memset(dpin, 63, sizeof dpin);
    dfs(0);
    
    return (answer > n ? -1 : answer);
  }
 
}
 
int best_path(int n, int k, int h[][2], int l[]) { 
  for (int i = 0; i < n - 1; ++i) { 
    int u = h[i][0], v = h[i][1], w = l[i];
    if (u > v) swap(u, v);
    ad[u].push_back({v, w});
    ad[v].push_back({u, w});
  }
  int sub = (n <= 1000 ? 2 : k <= 100 ? 3 : 4);
  if (sub == 2) return sub2::solve(n, k);
  if (sub == 3) return sub3::solve(n, k);
  return -1;
} 
 
#ifdef LOCAL
#define MAX_AA 500000
static int AA, K;
static int H[MAX_AA][2];
static int L[MAX_AA];
static int solution;
 
#define int long long
mt19937_64 rng(8384815663);
int rnd(int l, int r) { return l + rng() % (r - l + 1); }
 
inline 
void my_assert(int e) {if (!e) abort();}
 
void read_input()
{
  // AA = rnd(2e5, 2e5), K = rnd(100, 100);
  cin >> AA >> K;
  for (int i = 0; i < AA - 1; ++i) { 
    // H[i][0] = rnd(i, i);
    // H[i][1] = i + 1;
    // L[i] = rnd(1, 100);
    cin >> H[i][0] >> H[i][1] >> L[i];
  }
  solution = -1;
  // cin >> solution;
}
 
int32_t main() {
  int ans;
  read_input();
  ans = best_path(AA,K,H,L);
  cout << ans << "\n";
 
  return 0;
}
#endif

• Subtask 1: 9 / 9
• Subtask 2: 12 / 12
• Subtask 3: 22 / 22
• Subtask 4: 0 / 57