Grokking the Coding Interview: Patterns for Coding Questions
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Reverse Level Order Traversal (easy)
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Problem Statement

Given the root of a binary tree, return the bottom-up level order traversal of its nodes' values. (i.e., the lowest level comes first in left to right order.)

Examples

Example 1

  • Input: root = [1, 2, 3, 4, 5, 6, 7]
  • Expected Output: [[4, 5, 6, 7], [2, 3], [1]]
  • Justification:
    • The third level has 4, 5, 6, and 7 nodes.
    • The second level has 2 and 3 nodes.
    • The first level has a single node with the value 1.

Example 2

  • Input: root = [12, 7, 1, null, 9, 10, 5]
  • Expected Output: [[9, 10, 5], [7, 1], [12]]
  • Justification:
    • The third level has 9, 10, and 5 nodes.
    • The second level has 7 and 1 nodes.
    • The first level has a single node with the value 12.

Example 3

  • Input: root = [6,5,2,null,null,1,6,3,56,3]
  • Expected Output: [[3,56,3],[1,6],[5,2],[6]]
  • Justification:
    • The fourth level has 3, 56, and 3 nodes.
    • The third level has 1, and 6 nodes.
    • The second level has 5 and 2 nodes.
    • The first level has a single node with the value 6.

Constraints:

  • The number of nodes in the tree is in the range [0, 2000].
  • -1000 <= Node.val <= 1000

Try it yourself

Try solving this question here:

Python3
Python3
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