LeetCode_108_SortedArrayToBST.cpp

/*
  108. Convert Sorted Array to Binary Search Tree

  Given an array where elements are sorted in ascending order, convert it to a height balanced BST.
  For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of
  the two subtrees of every node never differ by more than 1.

  Example:
  Given the sorted array: [-10,-3,0,5,9],
  One possible answer is: [0,-3,9,-10,null,5], which represents the following height balanced BST:

      0
     / \
   -3   9
   /   /
 -10  5

*/

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
  TreeNode* convertToBst( vector<int> &nums, int start, int end ) {
    if( start > end ) {
      return NULL;
    }
    int mid = ( start + end + 1)/2;
    TreeNode *node = new TreeNode( nums[ mid ] );
    node->left = convertToBst( nums, start, mid - 1 );
    node->right = convertToBst( nums, mid + 1, end );
    return node;
  }
    
  TreeNode* sortedArrayToBST(vector<int>& nums) {
    return convertToBst( nums, 0, nums.size() - 1 );
  }
};