/*
* @lc app=leetcode.cn id=145 lang=typescript
*
* [145] 二叉树的后序遍历
*/
// @lc code=start
/**
* Definition for a binary tree node.
* class TreeNode {
* val: number
* left: TreeNode | null
* right: TreeNode | null
* constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
* this.val = (val===undefined ? 0 : val)
* this.left = (left===undefined ? null : left)
* this.right = (right===undefined ? null : right)
* }
* }
*/
function postorderTraversal(root: TreeNode | null): number[] {}
// @lc code=end
function postorderTraversal(root: TreeNode | null): number[] {
let res: number[] = []
while (root) {
if (root.right) {
let pre = root.right
while (pre.left && pre.left !== root) {
pre = pre.left!
}
if (!pre.left) {
pre.left = root
res.push(root.val)
root = root.right
} else {
root = root.left
}
} else {
res.push(root.val)
root = root.left
}
}
return res.reverse()
}
test.each([
{ input: { root: [1, null, 2, 3] }, output: [3, 2, 1] },
{ input: { root: [] }, output: [] },
{ input: { root: [1] }, output: [1] },
{ input: { root: [1, null, 2] }, output: [2, 1] },
{ input: { root: [1, 2] }, output: [2, 1] },
{ input: { root: [3, 1, 2] }, output: [1, 2, 3] },
])('input: root = $input.root', ({ input: { root }, output }) => {
expect(postorderTraversal(BinaryTree.deserialize(root))).toEqual(output)
})