547. Friend Circles

https://leetcode.com/problems/friend-circles/description/

class UnionFound {
public:
    vector<int> v;
    int cnt;
    UnionFound(int n) {
        v = vector<int>(n);
        for (int i = 0; i < n; i++)
            v[i] = i;
        cnt = n;
    }
    int GetParent(int i) {
        if (v[i] == i)  return i;
        return v[i] = GetParent(v[i]);
    }
    void Union(int p, int c) {
        int pp = GetParent(p);
        int cp = GetParent(c);
        if (pp != cp) {
            v[cp] = v[pp];
            cnt--;
        }
    }
};

class Solution {
public:
    int findCircleNum(vector<vector<int>>& M) {
        int m = M.size();   if (m == 0) return 0;
        UnionFound uf(m);
        for (int i = 0; i < m; i++)
            for (int j = i+1; j < m; j++)
                if (M[i][j] == 1)
                    uf.Union(i, j);
        return uf.cnt;
    }
};