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 {
public:
    TreeNode* mergeTrees(TreeNode* t1, TreeNode* t2) {
        
        //add the values of t2 onto t1
        
        if(t1==NULL){
            return t2;
        }else if(t2==NULL){
            return t1;
        }else{ 
            
            //t1!=NULL && t2!=NULL
            //use t1 as final result
            
            t1->val += t2->val;
            t1->left = mergeTrees(t1->left, t2->left);
            t1->right = mergeTrees(t1->right, t2->right);
            return t1;
        }
    }
};