Maximum Binary Tree — LeetCode 654 Python Solution

The problem

You are given an integer array nums with no duplicates. A maximum binary tree can be built recursively from nums using the following algorithm: Create a root node whose value is the maximum value in nums.

Example

Input

nums = [3,2,1,6,0,5]

Output

[6,3,5,null,2,0,null,null,1]

Explanation

The recursive calls are as follow:

Python solution

# 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 constructMaximumBinaryTree(self, nums: List[int]) -> Optional[TreeNode]:
        def dfs(nums):
            if not nums:
                return None
            val = max(nums)
            i = nums.index(val)
            root = TreeNode(val)
            root.left = dfs(nums[:i])
            root.right = dfs(nums[i + 1 :])
            return root

        return dfs(nums)

Complexity

Pattern: Stack

When the most recent unresolved thing is the one that matters, use a stack. LeetCode 654. Maximum Binary Tree is filed here because LeetCode tags it Stack, which is the vocabulary this hub collects.

The stack guide has the Python template for the pattern and the 194 LeetCode problems that use it.

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