number of connected components in an undirected graph solution

Author: yhkee0404

number-of-connected-components-in-an-undirected-graph/yhkee0404.kt

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+class Solution {
+    /**
+     * @param n: the number of vertices
+     * @param edges: the edges of undirected graph
+     * @return: the number of connected components
+     */
+    fun countComponents(n: Int, edges: Array<IntArray>): Int {
+        // write your code here
+        val adj = List(n) {mutableListOf<Int>()}
+        edges.forEach {
+                    adj[it[0]].add(it[1])
+                    adj[it[1]].add(it[0])
+                }
+        val visited = MutableList(n) {false} // T(V, E) = S(V, E) = O(V + E)
+        val stack = mutableListOf<Int>()
+        var ans = 0
+        for (i in 0 until n) {
+            if (visited[i]) {
+                continue
+            }
+            ans++
+            visited[i] = true
+            stack.add(i)
+            while (! stack.isEmpty()) {
+                val u = stack.removeLast()
+                adj[u].filter {! visited[it]}
+                        .forEach {
+                            visited[it] = true
+                            stack.add(it)
+                        }
+            }
+        }
+        return ans
+    }
+}