Leetcode654. Maximum Binary Tree

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

The root is the maximum number in the array.
The left subtree is the maximum tree constructed from left part subarray divided by the maximum number.
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:
The size of the given array will be in the range [1,1000].

找最大值，然后左右两边递归。

package leetcode;

/**
 * Created by linjian on 17/8/9.
 */
public class Leetcode654 {
    public static TreeNode constructMaximumBinaryTree(int[] nums) {
        if (nums.length == 0 ) return null;
        return subConstructMaximumBinaryTree(nums,0,nums.length-1);

    }
    public static TreeNode subConstructMaximumBinaryTree(int[] nums,int start,int end){
        if (start > end) return null;
        int max = Integer.MIN_VALUE;
        int index = 0;
        for (int i = start; i <= end; i++){
            if (max < nums[i]){
                max = nums[i];
                index = i;
            }
        }
        TreeNode root = new TreeNode(max);
        root.left =  subConstructMaximumBinaryTree(nums,0,index-1);
        root.right =  subConstructMaximumBinaryTree(nums,index+1,end);
        return root;
    }

}