Alex_tz307

USACO 2018 January Contest, Gold Problem 1. MooTube

Apr 15th, 2021
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  1. #include <bits/stdc++.h>
  2.  
  3. using namespace std;
  4.  
  5. ifstream fin("mootube.in");
  6. ofstream fout("mootube.out");
  7.  
  8. struct edge {
  9.   int u, v, w;
  10.  
  11.   void read() {
  12.     fin >> u >> v >> w;
  13.   }
  14.  
  15.   bool operator < (const edge &A) const {
  16.     return w > A.w;
  17.   }
  18. };
  19.  
  20. struct qry {
  21.   int k, v, ind;
  22.  
  23.   bool operator < (const qry &A) const {
  24.     return k > A.k;
  25.   }
  26. };
  27.  
  28. struct DSU {
  29.   vector<int> p, r;
  30.  
  31.   DSU(int N) {
  32.     p.resize(N + 1);
  33.     r.assign(N + 1, 1);
  34.     iota(p.begin(), p.end(), 0);
  35.   }
  36.  
  37.   int get(int x) {
  38.     if (x == p[x])
  39.       return x;
  40.     return p[x] = get(p[x]);
  41.   }
  42.  
  43.   int get_size(int u) {
  44.     return r[get(u)];
  45.   }
  46.  
  47.   bool unite(int u, int v) {
  48.     int x = get(u), y = get(v);
  49.     if (x == y)
  50.       return false;
  51.     if (r[x] > r[y]) {
  52.       p[y] = x;
  53.       r[x] += r[y];
  54.     } else {
  55.       p[x] = y;
  56.       r[y] += r[x];
  57.     }
  58.     return true;
  59.   }
  60. };
  61.  
  62. void solve() {
  63.   int N, Q;
  64.   fin >> N >> Q;
  65.   vector<edge> edges(N - 1);
  66.   for (edge &e : edges)
  67.     e.read();
  68.   sort(edges.begin(), edges.end());
  69.   vector<qry> queries(Q);
  70.   for (int i = 0; i < Q; ++i) {
  71.     fin >> queries[i].k >> queries[i].v;
  72.     queries[i].ind = i;
  73.   }
  74.   sort(queries.begin(), queries.end());
  75.   vector<int> sol(Q);
  76.   int p = 0;
  77.   DSU tree(N);
  78.   for (const qry &q : queries) {
  79.     while (p < N - 1 && edges[p].w >= q.k) {
  80.       tree.unite(edges[p].u, edges[p].v);
  81.       ++p;
  82.     }
  83.     sol[q.ind] = tree.get_size(q.v) - 1;
  84.   }
  85.   for (const int &x : sol)
  86.     fout << x << '\n';
  87. }
  88.  
  89. void close_files() {
  90.   fin.close();
  91.   fout.close();
  92. }
  93.  
  94. int main() {
  95.   solve();
  96.   close_files();
  97.   return 0;
  98. }
  99.  
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