Count the Number of Complete Components
<p>You are given an integer <code>n</code>. There is an <strong>undirected</strong> graph with <code>n</code> vertices, numbered from <code>0</code> to <code>n - 1</code>. You are given a 2D integer array <code>edges</code> where <code>edges[i] = [a<sub>i</sub>, b<sub>i</sub>]</code> denotes that there exists an <strong>undirected</strong> edge connecting vertices <code>a<sub>i</sub></code> and <code>b<sub>i</sub></code>.</p>

<p>Return <em>the number of <strong>complete connected components</strong> of the graph</em>.</p>

<p>A <strong>connected component</strong> is a subgraph of a graph in which there exists a path between any two vertices, and no vertex of the subgraph shares an edge with a vertex outside of the subgraph.</p>

<p>A connected component is said to be <b>complete</b> if there exists an edge between every pair of its vertices.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<p><strong class="example"><img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/2600-2699/2685.Count%20the%20Number%20of%20Complete%20Components/images/screenshot-from-2023-04-11-23-31-23.png" style="width: 671px; height: 270px;" /></strong></p>

<pre>
<strong>Input:</strong> n = 6, edges = [[0,1],[0,2],[1,2],[3,4]]
<strong>Output:</strong> 3
<strong>Explanation:</strong> From the picture above, one can see that all of the components of this graph are complete.
</pre>

<p><strong class="example">Example 2:</strong></p>

<p><strong class="example"><img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/2600-2699/2685.Count%20the%20Number%20of%20Complete%20Components/images/screenshot-from-2023-04-11-23-32-00.png" style="width: 671px; height: 270px;" /></strong></p>

<pre>
<strong>Input:</strong> n = 6, edges = [[0,1],[0,2],[1,2],[3,4],[3,5]]
<strong>Output:</strong> 1
<strong>Explanation:</strong> The component containing vertices 0, 1, and 2 is complete since there is an edge between every pair of two vertices. On the other hand, the component containing vertices 3, 4, and 5 is not complete since there is no edge between vertices 4 and 5. Thus, the number of complete components in this graph is 1.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= n &lt;= 50</code></li>
	<li><code>0 &lt;= edges.length &lt;= n * (n - 1) / 2</code></li>
	<li><code>edges[i].length == 2</code></li>
	<li><code>0 &lt;= a<sub>i</sub>, b<sub>i</sub> &lt;= n - 1</code></li>
	<li><code>a<sub>i</sub> != b<sub>i</sub></code></li>
	<li>There are no repeated edges.</li>
</ul>
Depth-First Search; Breadth-First Search; Union Find; Graph
func countCompleteComponents(n int, edges [][]int) (ans int) {
	g := make([][]int, n)
	vis := make([]bool, n)
	for _, e := range edges {
		a, b := e[0], e[1]
		g[a] = append(g[a], b)
		g[b] = append(g[b], a)
	}
	var dfs func(int) (int, int)
	dfs = func(i int) (int, int) {
		vis[i] = true
		x, y := 1, len(g[i])
		for _, j := range g[i] {
			if !vis[j] {
				a, b := dfs(j)
				x += a
				y += b
			}
		}
		return x, y
	}
	for i := range vis {
		if !vis[i] {
			a, b := dfs(i)
			if a*(a-1) == b {
				ans++
			}
		}
	}
	return
}