leetcode

Solution to some Leetcode problems written in C++
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2316.cpp (1039B)

      1 class UnionFind {
      2     int n, cnt = n;
      3     vector<int> root, size;
      4 
      5   public:
      6     UnionFind(int n) : n(n), root(n), size(n, 1) { iota(root.begin(), root.end(), 0); }
      7 
      8     int find(int x) {
      9         while (x != root[x])
     10             x = root[x] = root[root[x]];
     11         return x;
     12     }
     13 
     14     void join(int x, int y) {
     15         x = find(x), y = find(y);
     16         if (x != y) {
     17             if (size[x] > size[y]) swap(x, y);
     18             root[x] = y;
     19             size[y] += size[x];
     20             cnt--;
     21         }
     22     }
     23 
     24     int count() { return cnt; }
     25     bool connected(int x, int y) { return find(x) == find(y); }
     26 
     27     long long count_unreachable() {
     28         long long res = 0;
     29 
     30         for (int i = 0; i < n; i++)
     31             if (root[i] == i) res += (long long)size[i] * (n - size[i]);
     32 
     33         return res / 2;
     34     }
     35 };
     36 
     37 class Solution {
     38   public:
     39     long long countPairs(int n, vector<vector<int>> &edges) {
     40         UnionFind uf(n);
     41         for (auto &e : edges)
     42             uf.join(e[0], e[1]);
     43         return uf.count_unreachable();
     44     }
     45 };