题解 | #将升序数组转化为平衡二叉搜索树#

这个相对链表就easy了。

import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 * }
 */

public class Solution {
    /**
     * 
     * @param num int整型一维数组 
     * @return TreeNode类
     */
    public TreeNode sortedArrayToBST (int[] num) {
        // write code here
        if(num.length == 0)
            return null;

        if(num.length==1)
            return new TreeNode(num[0]);

        int left = 0 ; 
        int right = num.length;
        int mid = right / 2;

        TreeNode root = new TreeNode(num[mid]);
        root.left = sortedArrayToBST(Arrays.copyOfRange(num , left , mid));
        root.right = sortedArrayToBST(Arrays.copyOfRange(num , mid + 1 , right));

        return root;
    }
}