Convert Sorted Array to Binary Search Tree
描述
Given an array where elements are sorted in ascending order, convert it to a height balanced BST.
分析
二分法。
代码
// Convert Sorted Array to Binary Search Tree
// 二分法，时间复杂度O(n)，空间复杂度O(logn)
public class Solution {
public TreeNode sortedArrayToBST (int[] nums) {
return sortedArrayToBST(nums, 0, nums.length);
}
private static TreeNode sortedArrayToBST (int[] nums, int begin, int end) {
int length = end - begin;
if (length < 1) return null; // 终止条件
// 三方合并
int mid = begin + length / 2;
TreeNode root = new TreeNode (nums[mid]);
root.left = sortedArrayToBST(nums, begin, mid);
root.right = sortedArrayToBST(nums, mid + 1, end);
return root;
}
}