Given a binary tree, collect a tree's nodes as if you were doing this: Collect and remove all leaves, repeat until the tree is empty.

Example:
Given binary tree

          1
         / \
        2   3
       / \     
      4   5

Returns[4, 5, 3], [2], [1].

Explanation:

1. Removing the leaves[4, 5, 3]would result in this tree:

          1
         / 
        2

1. Now removing the leaf[2]would result in this tree:

          1

1. Now removing the leaf[1]would result in the empty tree:

          []

Returns[4, 5, 3], [2], [1].

Credits:
Special thanks to@elmirapfor adding this problem and creating all test cases.

tag: binary tree

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public List<List<Integer>> findLeaves(TreeNode root) {
        List<List<Integer>> ans = new ArrayList<>();
        if (root == null) return ans;

        dfs(root, ans);

        return ans;
    }

    private int dfs(TreeNode root, List<List<Integer>> ans){
        if (root == null) return 0;

        int height = 1 + Math.max(dfs(root.left, ans), dfs(root.right, ans));
        if (ans.size() < height){
            ans.add(new ArrayList<>());
        }
        ans.get(height - 1).add(root.val);

        return height;
    }
}