Invert Binary Tree

Leetcode Problem 226: Invert Binary Tree

Problem Summary

Given the root of a binary tree, invert the tree (produce its mirror image) by recursively swapping the left and right subtrees of every node, and return the root.

    4               4
   / \    -->      / \
  2   7           7   2
 / \ / \         / \ / \
1  3 6  9       9  6 3  1

Constraints:

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

Techniques

• Tree
• Depth-First Search
• Breadth-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 invertTree(root: TreeNode | null): TreeNode | null {
    if (root === null) {
        return root
    }

    const leftNode = invertTree(root.left)
    const rightNode = invertTree(root.right)

    root.left = rightNode
    root.right = leftNode

    return root
}