Binary Tree Inorder Traversal

Leetcode Problem 94: Binary Tree Inorder Traversal

Problem Summary

Given the root of a binary tree, return its nodes' values in in-order traversal order (left subtree → root → right subtree).

Constraints:

• The tree has between 0 and 100 nodes.
• Node values are integers in the range [-100, 100].

Techniques

• Stack
• Tree
• Depth-First Search
• Binary Tree

Solution

export 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 inorderTraversal(root: TreeNode | null): number[] {
    let stack: TreeNode[] = []
    let result: number[] = []
    let current = root

    while (current || stack.length > 0) {
        while (current) {
            stack.push(current)
            current = current.left
        }

        current = stack.pop()!
        result.push(current.val)
        current = current.right
    }

    return result
}