给予一个从小到大的数组, 构建一颗二叉平衡树, 即每个节点的两个子树的深度不能相差超过 1.
例 :
给予数组: [-10, -3, 0, 5, 9]
返回以下树都是符合条件的:
0
/ \
-3 9
/ /
-10 5
0
/ \
-10 5
\ \
-3 9
这道题有点类似于二分查找法, 即对二叉搜索树的反向推导, 每次取数组最中间的节点最为中节点, 左侧为左子树的内容, 右侧为右子树的内容, 直到不再存在子树.
import util.TreeNode;
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public TreeNode sortedArrayToBST(int[] nums) {
return helper(nums, 0, nums.length - 1);
}
private TreeNode helper(int[] nums, int start, int end) {
if (start > end) {
return null;
}
int mid = (start + end) / 2;
TreeNode node = new TreeNode(nums[mid]);
node.left = helper(nums, start, mid - 1);
node.right = helper(nums, mid + 1, end);
return node;
}
}
Runtime: 0 ms, faster than 100.00% of Java online submissions for Convert Sorted Array to Binary Search Tree. Memory Usage: 35.8 MB, less than 99.88% of Java online submissions for Convert Sorted Array to Binary