AC https://leetcode-cn.com/problems/binary-tree-postorder-traversal

Author: AaronLinRC

src/main/kotlin/TreeNode.kt

@@ -0,0 +1,4 @@
+class TreeNode(var `val`: Int) {
+    var left: TreeNode? = null
+    var right: TreeNode? = null
+}

src/main/kotlin/leetcode/binary-tree-postorder-traversal/Solution.kt

@@ -0,0 +1,20 @@
+package leetcode.`binary-tree-postorder-traversal`
+
+import TreeNode
+
+class Solution {
+    fun postorderTraversal(root: TreeNode?): List<Int> {
+        val arrayList = arrayListOf<Int>()
+        travel(root, arrayList)
+        return arrayList
+    }
+
+    private fun travel(treeNode: TreeNode?, list: ArrayList<Int>): List<Int> {
+        if (treeNode == null) return list
+//        print(treeNode.`val`)
+        travel(treeNode.left, list)
+        travel(treeNode.right, list)
+        list.add(treeNode.`val`)
+        return list
+    }
+}

src/main/kotlin/util/ListNode.kt

@@ -1 +1,21 @@
 package util
+
+import ListNode
+import java.util.TreeSet
+
+
+fun ListNode.print() {
+    val set = TreeSet<ListNode>()
+    var exploreP: ListNode? = this
+    var count = 1
+    while (exploreP != null) {
+        print(exploreP.`val`.toString() + " ")
+        if (set.contains(exploreP)) {
+            print("is a loop linked list,back to ${set.indexOfFirst { it == exploreP }}")
+        } else {
+            set.add(exploreP)
+        }
+        exploreP = exploreP.next
+        count++
+    }
+}