617-merge-two-binary-trees.cpp

class Solution {
public:
    TreeNode* mergeTrees(TreeNode* t1, TreeNode* t2) {
        if (!t1 && !t2) return NULL;
        if (!t1 && t2) return t2;
        if (t1 && !t2) return t1;
        t1->val = t1->val + t2->val;
        t1->left = mergeTrees(t1->left, t2->left);
        t1->right = mergeTrees(t1->right, t2->right);
        return t1;
    }
};