Today I have done leetcode's June LeetCoding Challenge with cpp.

June LeetCoding Challenge 26

Description

Balance a Binary Search Tree

Given the root of a binary search tree, return a balanced binary search tree with the same node values. If there is more than one answer, return any of them.

A binary search tree is balanced if the depth of the two subtrees of every node never differs by more than 1.

Example 1:

Input: root = [1,null,2,null,3,null,4,null,null]
Output: [2,1,3,null,null,null,4]
Explanation: This is not the only correct answer, [3,1,4,null,2] is also correct.

Example 2:

Input: root = [2,1,3]
Output: [2,1,3]

Constraints:

• The number of nodes in the tree is in the range [1, 104].
• 1 <= Node.val <= 105

Solution

class Solution {
  void visit(vector<int> &nums, TreeNode *root) {
    if(!root) return;
    visit(nums, root->left);
    nums.push_back(root->val);
    visit(nums, root->right);
  }
  TreeNode* build(const vector<int> &nums, int begin, int end) {
    if(begin > end) return nullptr;
    int mid = (begin + end) / 2;
    return new TreeNode(nums[mid], build(nums, begin, mid - 1), build(nums, mid + 1, end));
  }
public:
  TreeNode* balanceBST(TreeNode* root) {
    vector<int> nums;
    visit(nums, root);
    return build(nums, 0, nums.size() - 1);
  }
};