[Algorithm] 94. Binary Tree Inorder Traversal iteratively approach

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */

function getLefts(root) {
    if (!root) {
        return [];
    }
    
    let result = [];
    let current = root;
    while(current) {
        result.push(current);
        current = current.left ;
    }
    
    return result;
}

/**
 * @param {TreeNode} root
 * @return {number[]}
 */
var inorderTraversal = function(root) {
    let lefts = getLefts(root);
    let result = [];
    while (lefts.length) {
        let newRoot = lefts.pop();
        result.push(newRoot.val);
        if (newRoot.right) {
            let newLefts = getLefts(newRoot.right);
            lefts = lefts.concat(newLefts)
        }
    }
    
    return result;
};