LeetCode:Convert Sorted Array to Binary Search Tree

题目描述：

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

思路：采用类似折半查找的方式找到当前根节点，则位于当前根节点左边的属于它的左子树部分，位于当前根节点右边的属于它的右子树部分。再采用同样的方法，递归地对当前根节点的左右子树做相同的处理。

代码：

TreeNode * Solution::sortedArrayToBST(vector<int> &num)
{
if(num.size() == 0)
return NULL;
return sortedArrayToBSTCmp(num,0,num.size()-1);
}

TreeNode * Solution::sortedArrayToBSTCmp(vector<int> &num,int head,int rear)
{
TreeNode * root = (TreeNode *)malloc(sizeof(TreeNode));
int mid = (head + rear) / 2;
root->val = num[mid];
if(mid + 1 <= rear)
root->right = sortedArrayToBSTCmp(num,mid+1,rear);
if(head <= mid - 1)
root->left = sortedArrayToBSTCmp(num,head,mid-1);
return root;
}