leetcode_108 Convert Sorted Array to Binary Search Tree(Tree)

Posted 2020-09-14

Given an array where elements are sorted in ascending order, convert it to a height balanced BST.

递归进行。每次找到排序数组的中点，中点左边的子排序数组构成左子树，中点右边的子排序数组构成右子树。

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public TreeNode sortedArrayToBST(int[] nums) {
        if(nums.length==0){
            return null;
        }
        TreeNode head=construct(nums,0,nums.length-1);
        return head;
    }
    
    public TreeNode construct(int[] nums,int low,int high){
        if(low>high){  //边界条件
            return null;
        }
        int mid=low+(high-low)/2;
        TreeNode node=new TreeNode(nums[mid]);
        node.left=construct(nums,low,mid-1);
        node.right=construct(nums,mid+1,high);
        return node;
    }
}