【leetcode】654. Maximum Binary Tree

题目如下：

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].

解题思路：题目不难，从72%通过率就能看出来。方法是找出数组的最大值并作为根节点，然后把数组以最大值为界分成左右两部分；之后再对左右两部分分别递归，直到数组被分割完成为止。

代码如下：

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def build(self,node,nums):
        v = max(nums)
        inx = nums.index(v)
        node.val = v

        ll = nums[:inx]
        rl = nums[inx+1:]
        if len(ll) > 0:
            left = TreeNode(None)
            node.left = left
            self.build(left,ll)
        if len(rl) > 0:
            right = TreeNode(None)
            node.right = right
            self.build(right,rl)

    def constructMaximumBinaryTree(self, nums):
        """
        :type nums: List[int]
        :rtype: TreeNode
        """
        root = TreeNode(None)
        self.build(root,nums)
        return root