Leetcode#108 Convert Sorted Array to Binary Search Tree

 1 TreeNode *buildBST(vector<int> &num, int i, int j) {
 2   if (i > j)
 3     return NULL;
 4         
 5   int m = (i + j) /2;
 6   TreeNode *node = new TreeNode(num[m]);
 7   node->left = buildBST(num, i, m - 1);
 8   node->right = buildBST(num, m + 1, j);
 9         
10   return node;
11 }
12 
13 TreeNode *sortedArrayToBST(vector<int> &num) {
14   return buildBST(num, 0, num.size() - 1);
15 }