654. 最大二叉树

class Solution {
    public TreeNode constructMaximumBinaryTree(int[] nums) {
        return make(nums, 0, nums.length-1);
        
        }
    
    public static TreeNode make(int[] a, int begin, int end){
        if(begin >= end){
            int target = (begin + end) / 2;
            TreeNode node1 = new TreeNode(a[target]);
            return node1;
        }
        //1. 找到最大的元素的位置
        int index = begin;
        for(int i=begin; i<=end; i++){
            if(a[i] > a[index]) index = i;
        }
        TreeNode node1 = new TreeNode(a[index]);
        if(index !=begin){
            //2.找左边
            node1.left = make(a, begin, index-1);
        }
        if(index != end){
            //3. 找右边
            node1.right = make(a, index+1, end);
        }
        return node1;
    }
    
}
 public class TreeNode {
     int val;
     TreeNode left;
     TreeNode right;
     TreeNode(int x) { val = x; }
 }