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();

     }

 };

巴特西

Number of Connected Components in an Undirected Graph -- LeetCode

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