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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
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1 --- 2 4
Given n = 5 and edges = [[0, 1], [1, 2], [3, 4]], return 2.
Example 2:
0 4
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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)
1 class Solution { 2 public: 3 int getFather(vector<int>& father, int i) { 4 if (father[i] == i) return i; 5 father[i] = getFather(father, father[i]); 6 return father[i]; 7 } 8 void merge(vector<int>& father, int i, int j) { 9 int fatherI = getFather(father, i); 10 int fatherJ = getFather(father, j); 11 father[fatherJ] = fatherI; 12 } 13 int countComponents(int n, vector<pair<int, int>>& edges) { 14 vector<int> father; 15 for (int i = 0; i < n; i++) father.push_back(i); 16 for (int i = 0, n = edges.size(); i < n; i++) 17 merge(father, get<0>(edges[i]), get<1>(edges[i])); 18 unordered_set<int> unions; 19 for (int i = 0; i < n; i++) unions.insert(getFather(father, i)); 20 return unions.size(); 21 } 22 };
Number of Connected Components in an Undirected Graph -- LeetCode
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原文地址：http://www.cnblogs.com/fenshen371/p/5786148.html
