/**
* 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 {number[][]}
*/
// O(NlogN) time for sorting, O(N) space for node heights
var findLeaves = function(root) {
 const nodeHeights = [];
 // Recursive function to get all the heights of each node
 const getHeight = (currentRoot) => {
   if (currentRoot === null) {
     return -1;
   }
   
   const leftHeight = getHeight(currentRoot.left);
   const rightHeight = getHeight(currentRoot.right);
   
   const currentHeight = Math.max(leftHeight, rightHeight) + 1;
   
   nodeHeights.push([currentHeight, currentRoot.val]);
   
   return currentHeight;
 };
 
 // Get the heights of all the nodes in the tree
 getHeight(root);
 
 // Sort the nodes by height in ascending order
 nodeHeights.sort((a, b) => a[0] - b[0]);
 
 // Build the leaves solution based on the sorted node heights
 const leavesHeights = [];
 let height = 0;
 let i = 0;
 while (i < nodeHeights.length) {
   const currentLeaves = [];
   // While we're on the same height, we keep adding to the current leaves array
   while (i < nodeHeights.length && nodeHeights[i][0] === height) {
     currentLeaves.push(nodeHeights[i][1]);
     i++;
   }
   leavesHeights.push(currentLeaves);
   height++;
 }
 
 return leavesHeights;
};