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

class Solution {
public:
    /**
     * 
     * @param t1 TreeNode类 
     * @param t2 TreeNode类 
     * @return TreeNode类
     */
    void function(TreeNode* t1, TreeNode* t2) {
        if(!t1 && !t2)
            return;
        t1->val += t2->val;
        
        if(t1->left && t2->left)
            function(t1->left, t2->left);
        if(!t1->left && t2->left) {
            t1->left = new TreeNode(0);
            function(t1->left, t2->left);
        }
        if(t1->left && !t2->left) {
            t2->left = new TreeNode(0);
            function(t1->left, t2->left);
        }
        if(t1->right && t2->right)
            function(t1->right, t2->right);
        if(!t1->right && t2->right) {
            t1->right = new TreeNode(0);
            function(t1->right, t2->right);
        }
        if(t1->right && !t2->right) {
            t2->right = new TreeNode(0);
            function(t1->right, t2->right);
        }
        return;
    }
    TreeNode* mergeTrees(TreeNode* t1, TreeNode* t2) {
        // write code here
        function(t1, t2);
        return t1;
    }
};