merge-two-binary-trees.cpp

/**
 * 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 traverse(TreeNode* root1, TreeNode* root2) {
        if (root1 && root2) root1->val = root1->val + root2->val;
        
        if (root1->left && root2->left) traverse(root1->left, root2->left);
        if (root1->right && root2->right) traverse(root1->right, root2->right);
        
        if (root2->left && !root1->left) root1->left = root2->left;
        if (root2->right && !root1->right) root1->right = root2->right;
    }
public:
    TreeNode* mergeTrees(TreeNode* root1, TreeNode* root2) {
        if (!root1) return root2;
        if (!root2) return root1;
        traverse(root1, root2);
        return root1;
    }
};