1. FriendCycle

class Solution {public:    int findCircleNum(vector
     
      
       >& M) {        int len = M.size();        if (len == 0) return 0;        vector
       
         parent(len, 0);        for (int i=0; i
        

&parent){ if (parent[pos] == pos) return pos; int root = findParent(parent[pos], parent); parent[pos] = root; return root; }};