323. Number of Connected Components in an Undirected Graph

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:

Input: n = 5 and edges = [[0, 1], [1, 2], [3, 4]]

0          3
|          |
1 --- 2    4

Output: 2

Example 2:

Input: n = 5 and edges = [[0, 1], [1, 2], [2, 3], [3, 4]]

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

Output:  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.

323. Number of Connected Components in an Undirected Graph
struct Solution;

struct UnionFind {
parent: Vec<usize>,
n: usize,
}

impl UnionFind {
fn new(n: usize) -> Self {
let parent = (0..n).collect();
UnionFind { parent, n }
}
fn find(&mut self, i: usize) -> usize {
let j = self.parent[i];
if i == j {
i
} else {
let k = self.find(j);
self.parent[i] = k;
k
}
}

fn union(&mut self, i: usize, j: usize) {
let i = self.find(i);
let j = self.find(j);
if i != j {
self.parent[i] = j;
self.n -= 1;
}
}
}

impl Solution {
fn count_components(n: i32, edges: Vec<Vec<i32>>) -> i32 {
let n = n as usize;
let mut uf = UnionFind::new(n);
for edge in edges {
let i = edge[0] as usize;
let j = edge[1] as usize;
uf.union(i, j);
}
uf.n as i32
}
}

#[test]
fn test() {
let n = 5;
let edges = vec_vec_i32![[0, 1], [1, 2], [3, 4]];
let res = 2;
assert_eq!(Solution::count_components(n, edges), res);
let n = 5;
let edges = vec_vec_i32![[0, 1], [1, 2], [2, 3], [3, 4]];
let res = 1;
assert_eq!(Solution::count_components(n, edges), res);
}