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

October LeetCoding Challenge 23

Description

Cousins in Binary Tree II

Given the root of a binary tree, replace the value of each node in the tree with the sum of all its cousins' values.

Two nodes of a binary tree are cousins if they have the same depth with different parents.

Return the root of the modified tree.

Note that the depth of a node is the number of edges in the path from the root node to it.

Example 1:

Input: root = [5,4,9,1,10,null,7]
Output: [0,0,0,7,7,null,11]
Explanation: The diagram above shows the initial binary tree and the binary tree after changing the value of each node.
- Node with value 5 does not have any cousins so its sum is 0.
- Node with value 4 does not have any cousins so its sum is 0.
- Node with value 9 does not have any cousins so its sum is 0.
- Node with value 1 has a cousin with value 7 so its sum is 7.
- Node with value 10 has a cousin with value 7 so its sum is 7.
- Node with value 7 has cousins with values 1 and 10 so its sum is 11.

Example 2:

Input: root = [3,1,2]
Output: [0,0,0]
Explanation: The diagram above shows the initial binary tree and the binary tree after changing the value of each node.
- Node with value 3 does not have any cousins so its sum is 0.
- Node with value 1 does not have any cousins so its sum is 0.
- Node with value 2 does not have any cousins so its sum is 0.

Constraints:

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

Solution

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
  void solve(vector<TreeNode*> roots){
    if(roots.empty()) return;
    int sum = 0;
    for(auto root : roots) {
      if(!root) continue;
      if(root->left) sum += root->left->val;
      if(root->right) sum += root->right->val;
    }

    vector<TreeNode*> children;
    for(auto root : roots) {
      int currentSum = 0;
      if(root->left) currentSum += root->left->val;
      if(root->right) currentSum += root->right->val;

      if(root->left) {
        root->left->val = sum - currentSum;
        children.push_back(root->left);
      }
      if(root->right) {
        root->right->val = sum - currentSum;
        children.push_back(root->right);
      }
    }
    solve(children);
  }
public:
  TreeNode* replaceValueInTree(TreeNode* root) {
    root->val = 0;
    solve({root});
    return root;
  }
};