108. Convert Sorted Array to Binary Search Tree | 有序数组生成平衡二叉搜索树

原创于 2017-02-23 10:56:36 发布 · 317 阅读

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本文介绍了一种将升序数组转换为高度平衡的二叉搜索树的方法。通过递归地选择中间元素作为根节点，确保左右子树的高度尽可能相同。

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

/**
 * 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) {
		TreeNode node = null;
		node = helper(nums, 0, nums.length - 1);
		return node;
	}

	public 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;
	}
}