Number of Connected Components in an Undirected Graph -- LeetCode

Given n nodes labeled from 0 to n - 1 and a list of undirected edges (each edge is a pair of nodes), write a function to find the number of connected components in an undirected graph.

Example 1:

     |          |
      ---     

Given n = 5 and edges = [[0, 1], [1, 2], [3, 4]], return 2.

Example 2:

     |           |
      ---  --- 

Given n = 5 and edges = [[0, 1], [1, 2], [2, 3], [3, 4]], return 1.

Note:
You can assume that no duplicate edges will appear in edges. Since all edges are undirected, [0, 1] is the same as [1, 0] and thus will not appear together in edges.

思路：并查集(Union find)

 class Solution {
 public:
     int getFather(vector<int>& father, int i) {
         if (father[i] == i) return i;
         father[i] = getFather(father, father[i]);
         return father[i];
     }
     void merge(vector<int>& father, int i, int j) {
         int fatherI = getFather(father, i);
         int fatherJ = getFather(father, j);
         father[fatherJ] = fatherI;
     }
     int countComponents(int n, vector<pair<int, int>>& edges) {
         vector<int> father;
         for (int i = ; i < n; i++) father.push_back(i);
         for (int i = , n = edges.size(); i < n; i++)
             merge(father, get<>(edges[i]), get<>(edges[i]));
         unordered_set<int> unions;
         for (int i = ; i < n; i++) unions.insert(getFather(father, i));
         return unions.size();
     }
 };