Number of Connected Components in an Undirected Graph

Author: eunhwa99

number-of-connected-components-in-an-undirected-graph/eunhwa99.kt

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+class Solution {
+    // Time Complexity: O(n + e)
+    // Space Complexity: O(n + e)
+    // n : number of nodes
+    // e : number of edges
+    fun countComponents(n: Int, edges: Array<IntArray>): Int {
+        val graph = Array(n) { mutableListOf<Int>() }
+        for (edge in edges) { // make graph
+            graph[edge[0]].add(edge[1])
+            graph[edge[1]].add(edge[0])
+        }
+        val visited = BooleanArray(n) // visited array
+        var count = 0 // number of connected components
+
+        for (i in 0 until n) {
+            if (!visited[i]) {
+                dfs(i, graph, visited)
+                count++
+            }
+        }
+        return count
+    }
+
+    fun dfs(node: Int, graph: Array<MutableList<Int>>, visited: BooleanArray) {
+        visited[node] = true
+        for (neighbor in graph[node]) {
+            if (!visited[neighbor]) {
+                dfs(neighbor, graph, visited)
+            }
+        }
+    }
+}