對於這種有返回的 dfs() 的遍歷方式還是不熟。


class Solution {
public:
    TreeNode* mergeTrees(TreeNode* t1, TreeNode* t2) {

        if (!t1 && !t2) {
            return NULL;
        }

        if (t1 && !t2) {
            return t1;
        }
        if (!t1 && t2) {
            return t2;
        }

        if (t1 && t2) {
            t1->val += t2->val;

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

        return t1;
    }
};

[Leetcode] Merge Two Binary Trees