108. 将有序数组转换为二叉搜索树

递归、二分

/**
 * 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 sortedArrayToBST(int[] nums) {
        TreeNode root = traval(nums,0,nums.length - 1);
        return root;
    }
    public TreeNode traval(int[] nums, int l, int r ) {
        if(l > r ) return null;
        int mid = l + ( (r - l ) >> 1);
        TreeNode root = new TreeNode(nums[mid] );
        root.left = traval(nums,l ,mid - 1);
        root.right = traval(nums, mid + 1, r);
        return root;
    }
}