Create 0116-populating-next-right-pointers-in-each-node.kt

Author: a93a

kotlin/0116-populating-next-right-pointers-in-each-node.kt

@@ -0,0 +1,62 @@
+// Time complexity O(n) and space complexity O(1) with Follow-up constraints, without using recursion
+class Solution {
+    fun connect(root: Node?): Node? {
+        var cur = root
+        var next = cur?.left
+
+        while (cur != null && next != null) {
+            cur?.left?.next = cur?.right
+            if (cur?.next != null)
+                cur?.right?.next = cur?.next?.left
+
+            cur = cur?.next
+            if (cur == null) {
+                cur = next
+                next = cur?.left
+            }
+        }
+        
+        return root
+    }
+}
+
+// Time complexity O(n) and space complexity O(1) with Follow-up constraints using recursion
+class Solution {
+    fun connect(root: Node?): Node? {
+        root?: return null
+
+        root.left?.let {
+            it.next = root.right
+            root.right?.let {
+                it.next = root.next?.left
+            }
+            connect(root.left)
+            connect(root.right)
+        }
+
+        return root
+    }
+}
+
+// Time complexity O(n) and space complexity O(logn)
+class Solution {
+    fun connect(root: Node?): Node? {
+        with (LinkedList<Pair<Node?, Int>>()) {
+            addLast(root to 0)
+
+            while (isNotEmpty()) {
+                repeat (size) {
+                    val (curNode, curLevel) = removeFirst()
+                    peekFirst()?.let { (nextNode, nextLevel) ->
+                        if (nextLevel == curLevel)
+                            curNode?.next = nextNode
+                    }
+                    curNode?.left?.let { addLast(it to (curLevel + 1)) }
+                    curNode?.right?.let { addLast(it to (curLevel + 1)) }
+                }
+            }
+        }
+
+        return root
+    }
+}