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:

     0          3
     |          |
     1 --- 2    4

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

Example 2:

     0           4
     |           |
     1 --- 2 --- 3

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 = 0; i < n; i++) father.push_back(i);
        for (int i = 0, n = edges.size(); i < n; i++)
            merge(father, get<0>(edges[i]), get<1>(edges[i]));
        unordered_set<int> unions;
        for (int i = 0; i < n; i++) unions.insert(getFather(father, i));
        return unions.size();
    }
};