654. Maximum Binary Tree (Medium)

Given an integer array with no duplicates. A maximum tree building on this array is defined as follow:

1. The root is the maximum number in the array.
2. The left subtree is the maximum tree constructed from left part subarray divided by the maximum number.
3. The right subtree is the maximum tree constructed from right part subarray divided by the maximum number.

Construct the maximum tree by the given array and output the root node of this tree.

Example 1:

Input: [3,2,1,6,0,5]
Output: return the tree root node representing the following tree:

      6
    /   
   3     5
        / 
     2  0   
       
        1

Note:

1. The size of the given array will be in the range [1,1000].

题意：对于给定的无重复元素的数组，

          1）根节点是数组中最大的元素；

　　   2）左半数组中最大的元素作为左子树的根；

　　   3）右半数组中最大的元素作为右子树的根；

思路：递归

class Solution:
    def constructMaximumBinaryTree(self, nums):
        """
        :type nums: List[int]
        :rtype: TreeNode
        """
        if not nums:
            return None
        max_num = max(nums)
        node = TreeNode(max_num)
        idx = nums.index(max_num)
        node.left = self.constructMaximumBinaryTree(nums[:idx])
        node.right = self.constructMaximumBinaryTree(nums[idx+1:])
        return node