最大二叉树

思路：

 1. 数组内只有一个元素时，直接构造节点返回；
 2. 构造递归方法，传入数组的范围；
 3. 寻找当前最大的元素，然后一这个节点为基准切割数组；
 4. 后续按元素切割方法递归进入下一轮切割。

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public TreeNode constructMaximumBinaryTree(int[] nums) {
        if(nums.length == 1){
            return new TreeNode(nums[0]);
        }

        return getBestTreeNode(nums,0,nums.length - 1);
    }

    private TreeNode getBestTreeNode(int[] nums,int left,int right){
        if(left > right){
            return null;
        }
        int best = left;
        for(int i = left + 1;i < right + 1;i++){
            if(nums[i] > nums[best]){
                best = i;
            }
        }
        TreeNode node = new TreeNode(nums[best]);
        node.left = getBestTreeNode(nums,left,best - 1);
        node.right = getBestTreeNode(nums,best + 1,right);
        return node;
    }
}