108. Convert Sorted Array to Bin

题目分析

代码

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    
    private TreeNode build(int[] nums, int start, int end) {
        // 注意结束条件
        if(start > end) {
            return null;
        }
        TreeNode node = new TreeNode(nums[(start + end) / 2]);
        node.left = build(nums, start, (start + end) / 2 - 1);
        node.right = build(nums, (start + end) / 2 + 1, end);
        return node;
    }
    
    public TreeNode sortedArrayToBST(int[] nums) {
        if(nums == null) {
            return null;
        }
        return build(nums, 0, nums.length - 1);
    }
}