[LeetCode]Convert Sorted Array to BST

很简单的二分。代码如下：

	/**
	* Definition for binary tree
	* public class TreeNode {
	* int val;
	* TreeNode left;
	* TreeNode right;
	* TreeNode(int x) { val = x; }
	* }
	*/
	public class Solution {
	public TreeNode sortedArrayToBST(int[] num) {
	if (num == null)
	return null;
	int len = num.length;
	return build(num, 0, len - 1);
	}
	private TreeNode build(int[] num, int lo, int hi) {
	if (lo > hi)
	return null;
	int mid = lo + (hi - lo) / 2;
	TreeNode node = new TreeNode(num[mid]);
	node.left = build(num, lo, mid - 1);
	node.right = build(num, mid + 1, hi);
	return node;
	}
	}

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