145. 二叉树的后序遍历 (二刷)

Author: w2xi

vs-lt/145.二叉树的后序遍历.js

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+/*
+ * @lc app=leetcode.cn id=145 lang=javascript
+ *
+ * [145] 二叉树的后序遍历
+ */
+
+import { node } from "webpack";
+
+// @lc code=start
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.left = (left===undefined ? null : left)
+ *     this.right = (right===undefined ? null : right)
+ * }
+ */
+/**
+ * @param {TreeNode} root
+ * @return {number[]}
+ */
+var postorderTraversal = function(root) {
+  // 递归
+  const result = [];
+  const postOrder = (node) => {
+    if (node) {
+      postOrder(node.left);
+      postOrder(node.right);
+      result.push(node.val);
+    }
+  }
+  postOrder(root);
+
+  return result;
+
+  // return postOrderIterate(root);
+};
+
+// 迭代
+// 中右左
+// => reverse
+// 左右中
+
+function postOrderIterate(root) {
+  if (!root) return [];
+  const result = [];
+  const stack = [root];
+
+  while (stack.length) {
+    node = stack.pop();
+    result.push(node.val);
+
+    node.left && stack.push(node.left);
+    node.right && stack.push(node.right);
+  }
+
+  return result.reverse();
+}
+// @lc code=end
+