MergeTwoBinaryTrees.cpp

// Recursive 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
{
public:
    TreeNode *mergeTrees(TreeNode *t1, TreeNode *t2)
    {
        if (t1 == NULL)
            return t2;
        if (t2 == NULL)
            return t1;

        t1->val += t2->val;
        t1->left = mergeTrees(t1->left, t2->left);
        t1->right = mergeTrees(t1->right, t2->right);

        return t1;
    }
};

// Time Complexity - O(m) -> m represents
// minimum no. of nodes that need to be traversed
// Space Complexity - O(m) -> depth of recursion tree
// can go upto m in case of a skewed tree
// while the average space complexity is O(logm)