101. Symmetric Tree

/**
* Problem statement: https://leetcode.com/problems/symmetric-tree/
*
* The first solution here is an iterative one. It's not as efficient or elegant as the recursive solution that follows.
*/

/* Iterative Solution */

function getNodesRight(node, stack) {
    if (node === null) return [null]
    return [...stack,
            node.val,
            ...getNodesRight(node.right, stack),
            ...getNodesRight(node.left, stack)]
}

function getNodesLeft(node, stack) {
    if (node === null) return [null]
    return [...stack,
            node.val,
            ...getNodesLeft(node.left, stack),
            ...getNodesLeft(node.right, stack)]
}

 /**
 * @param {TreeNode} root
 * @return {boolean}
 */
var isSymmetric = function(root) {
    if (root === null) return true

    const leftNodes = getNodesLeft(root.left, [])
    const rightNodes = getNodesRight(root.right, [])

    for (let i = 0; i < leftNodes.length; i++) {
        if (leftNodes[i] !== rightNodes[i]) return false
    }

    return true
}


/* Recursive Solution */

function isMirror(left, right) {
    if (left === null && right == null) return true
    if (left === null || right === null) return false
    if (left.val !== right.val) return false
    return isMirror(left.left, right.right) && isMirror(left.right, right.left)
}

 /**
 * @param {TreeNode} root
 * @return {boolean}
 */
var isSymmetric = function(root) {
    if (root === null) return true
    return isMirror(root.left, root.right)
}