【convert-sorted-array-to-binary-search-tree 】

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

思路：和鏈表轉化成平衡二叉樹的思路一樣，不過數組找中間位置比較簡單

class Solution {
public:
	TreeNode* sortedArrayToBST(vector<int>& num)
	{
		if (num.empty())
		{
			return NULL;
		}

		return vecToBST(0, num.size()-1, num);
	}

	TreeNode* vecToBST(int low, int high, vector<int> v)
	{
		int mid;
		mid = (low+high+1)/2;//找中間位置
		TreeNode* root = new TreeNode(v[mid]);
		if (mid-1>=low)
		{
			root->left= vecToBST(low, mid-1, v);
		}
		if (mid+1<=high)
		{
			root->right = vecToBST(mid+1, high, v);
		}

		return root;
	}
};