solution.cpp

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution 
{
public:
    TreeNode* createTree(vector<int> &num,int left, int right)
    {
        if(left > right)
            return NULL;
        int mid = (left+right)/2;
        
        TreeNode *leftNode = createTree(num, left, mid - 1);
        TreeNode *rightNode = createTree(num, mid + 1, right);
        
        TreeNode *node = new TreeNode(num[mid]);
        
        node->left = leftNode;
        node->right = rightNode;

        return node;
    }

    TreeNode *sortedArrayToBST(vector<int> &num) 
    {
        return createTree(num,0,num.size()-1);
    }
};