LeetCode——Convert Sorted Array to Binary Search Tree

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

原题链接：https://oj.leetcode.com/problems/convert-sorted-array-to-binary-search-tree/

题目：给定一个升序排列元素的数组，将其转换成高度平衡的二叉树。

思路：已经排序。则从中间劈开，中间元素为树的根，左右递归构建。

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