Description:

题目大意：合并两棵二叉树。合并规则是：都存在的结点，就将结点值加起来，否则空的位置就由另一个树的结点来代替。

解题思路:

算法标签：递归

代码:

/**
 * struct TreeNode {
 *	int val;
 *	struct TreeNode *left;
 *	struct TreeNode *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;
    }
};