366 Find Leaves of Binary Tree

🔀 Pick One

Given the root of a binary tree, collect a tree's nodes as if you were doing this:

  • Collect all the leaf nodes.
  • Remove all the leaf nodes.
  • Repeat until the tree is empty.

Example 1:

    1
   / \          1
  2   3   =>   /    =>   1
 / \          2
4   5

Input: root = [1,2,3,4,5]
Output: [[4,5,3],[2],[1]]
Explanation:
[[3,5,4],[2],[1]] and [[3,4,5],[2],[1]] are also considered correct answers
since per each level it does not matter the order on which elements are returned.

Example 2:

Input: root = [1]
Output: [[1]]

Constraints:

  • The number of nodes in the tree is in the range [1, 100].
  • -100 <= Node.val <= 100
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# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def findLeaves(self, root: Optional[TreeNode]) -> List[List[int]]:
        def dfs(node: Optional[TreeNode]) -> int:
            if not node:
                return 0
            cur_level = max(dfs(node.left), dfs(node.right)) + 1
            d[cur_level].append(node.val)
            return cur_level
        
        d = defaultdict(list)
        dfs(root)
        return [vals for _, vals in sorted(d.items(), key=lambda n: n[0])]