617. Merge Two Binary Trees

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    TreeNode* mergeTrees(TreeNode* t1, TreeNode* t2) {
        if(t1 == NULL && t2 == NULL){
            return NULL;
        }
        int val = 0;
        TreeNode* root = new TreeNode(0);
        if(t1 != NULL && t2!= NULL){
            val = t1->val+t2->val;
            root->val = val;
            root->left = mergeTrees(t1->left,t2->left);
            root->right = mergeTrees(t1->right,t2->right);
            
        }else if(t1 != NULL){
            root->val = t1->val;   
            root->left = mergeTrees(t1->left,NULL);
            root->right = mergeTrees(t1->right,NULL);
        }else if(t2!= NULL){
            root->val = t2->val;
            root->left = mergeTrees(NULL,t2->left);
            root->right = mergeTrees(NULL,t2->right);
        }
        // cout << root->val << endl;
        
        return root;
        
    }
};