Given the root of a binary tree, return the lowest common ancestor of its deepest leaves. Recall that: The node of a binary tree is a leaf if and only if it has no children The depth of the root of the tree is 0. if the depth of a node is d, the de

lcaDeepestLeaves.js

/**
 * 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 {TreeNode}
 */
var lcaDeepestLeaves = function(root) {
    // Variable to track the maximum depth of the tree
    let maxDepth = 0;

    function findDepth(node, depth) {
        if (node !== null) {
            // Update the maximum depth seen so far
            maxDepth = Math.max(depth, maxDepth);

            // Recurse into the left and right subtrees
            findDepth(node.left, depth + 1);
            findDepth(node.right, depth + 1);
        }
    }

    // First pass to calculate the maximum depth of the tree (0(N))
    findDepth(root, 0);

    function findLCA(node, depth) {
        if (node === null) {
            // Return null for an empty node
            return null;
        }

        if (depth === maxDepth) {
            // If the current node is at the maximum depth, it's part of the deepest leaves
            return node;
        }

        // Recurse into the left and right subtrees
        const leftLCA = findLCA(node.left, depth + 1);
        const rightLCA = findLCA(node.right, depth + 1);

        // Determine the LCA based on the results from the left and right subtrees
        if (leftLCA !== null && rightLCA !== null) {
            // If both subtrees have deepest leaves, the current node is their LCA
            return node;
        } else if (leftLCA !== null) {
            // Only the left subtree contains deepest leaves
            return leftLCA;
        } else if (rightLCA !== null) {
            // Only the right subtree contains deepest leaves
            return rightLCA;
        }

        // If neither subtree contains the deepest leaves, return null
        return null;
    }

    // Second pass to find the LCA of the deepest leaves (0(N))
    return findLCA(root, 0);
};