lk654.java

/**
 * 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) {
        return build(nums, 0, nums.length - 1);
    }


    TreeNode build(int[] nums, int lo, int hi) {
        if (lo > hi) {
            return null;
        }

        int index = -1, maxVal = Integer.MIN_VALUE;
        for (int i = lo; i<=hi; i++){
            if (maxVal < nums[i]) {
                index = i;
                maxVal = nums[i];
            }
        }
        TreeNode root = new TreeNode(maxVal);

        root.left = build(nums, lo, index - 1);
        root.right = build(nums, index + 1, hi);

        return root;
    }
}