107-Binary_Tree_Level_Order_Traversal_II.html

<html>
<script>
/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number[][]}
 */
var levelOrderBottom = function(root) {
    let traverseArr = [];
    let traverse = function(node, level){
        if(!node) return
        else{
            if(traverseArr.length < level+1){
                traverseArr.push([node.val]);
            }else{
                traverseArr[level].push(node.val);
            }
            traverse(node.left, level+1);
            traverse(node.right, level+1);
        }
    }
    traverse(root, 0);
    return traverseArr.reverse();
};
levelOrderBottom([3,9,20,null,null,15,7]);
</script>
</html>