题目
题目链接
题解
/**
* 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) {
if (nums == null || nums.length == 0) {
return null;
}
return divideAndRule(nums, 0, nums.length - 1);
}
/**
* 分治算法,传入数组的左边界和右边界,闭区间
*/
private TreeNode divideAndRule(int[] nums, int start, int end) {
if (start == end) {
return new TreeNode(nums[start]);
}
int mid = (start + end) / 2;
TreeNode left = null;
TreeNode right = null;
if (start <= mid - 1) {
left = divideAndRule(nums, start, mid - 1);
}
if (mid + 1 <= end) {
right = divideAndRule(nums, mid + 1, end);
}
return new TreeNode(nums[mid], left, right);
}
}