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

December LeetCoding Challenge 20

Description

Reverse Odd Levels of Binary Tree

Given the root of a perfect binary tree, reverse the node values at each odd level of the tree.

For example, suppose the node values at level 3 are [2,1,3,4,7,11,29,18], then it should become [18,29,11,7,4,3,1,2].

Return the root of the reversed tree.

A binary tree is perfect if all parent nodes have two children and all leaves are on the same level.

The level of a node is the number of edges along the path between it and the root node.

Example 1:

Input: root = [2,3,5,8,13,21,34]
Output: [2,5,3,8,13,21,34]
Explanation: 
The tree has only one odd level.
The nodes at level 1 are 3, 5 respectively, which are reversed and become 5, 3.

Example 2:

Input: root = [7,13,11]
Output: [7,11,13]
Explanation: 
The nodes at level 1 are 13, 11, which are reversed and become 11, 13.

Example 3:

Input: root = [0,1,2,0,0,0,0,1,1,1,1,2,2,2,2]
Output: [0,2,1,0,0,0,0,2,2,2,2,1,1,1,1]
Explanation: 
The odd levels have non-zero values.
The nodes at level 1 were 1, 2, and are 2, 1 after the reversal.
The nodes at level 3 were 1, 1, 1, 1, 2, 2, 2, 2, and are 2, 2, 2, 2, 1, 1, 1, 1 after the reversal.

Constraints:

The number of nodes in the tree is in the range [1, 2¹⁴].
0 <= Node.val <= 10⁵
root is a perfect binary tree.

Solution

class Solution {
  vector<vector<int>> values;
  void preorder(TreeNode* root, bool modify = false, int level = 0) {
    if(!root) return;
    if(values.size() <= level / 2) values.push_back({});
    if(level & 1) {
      if(!modify) {
        values[level / 2].push_back(root->val);
      } else {
        root->val = values[level / 2].back();
        values[level / 2].pop_back();
      }
    }
    preorder(root->left, modify, level + 1);
    preorder(root->right, modify, level + 1);
  }
public:
  TreeNode* reverseOddLevels(TreeNode* root) {
    preorder(root);
    preorder(root, true);

    return root;
  }
};

// Accepted
// 57/57 cases passed (0 ms)
// Your runtime beats 100 % of cpp submissions
// Your memory usage beats 63.46 % of cpp submissions (78.7 MB)

2024-12-20 Daily Challenge

December LeetCoding Challenge 20

Description

Solution