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();
}
};
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