# Why runtime error? I can run the code on my computer

• the test case of runtime errot is [1,2,null,3]

``````class Solution {
public:
void flatten(TreeNode* root) {
if(!root)
return;

myflatten(root,nullptr);
}

void myflatten(TreeNode* root,TreeNode* bro)
{
if(!root->left&&!root->right&&!bro)
return;
if(!root->left&&!root->right)
{
root->right=bro;
myflatten(bro,nullptr);
}
else if(root->left&&root->right)
{
TreeNode* temp=nullptr;

temp=root->right;
root->right=root->left;
myflatten(root->right,nullptr);
myflatten(root->right,temp);

}
else if(root->left)
{
root->right=root->left;
root->left=nullptr;
myflatten(root->right,bro);
}
else if(root->right)
{
myflatten(root->right,bro);
}
}

};``````

• Happened to me as well. For me, my mistake was that I was pointing the left and right pointers of a TreeNode to the same TreeNode.

• so you mean it's my mistake, not the OJ's ?

• Hey, I verified your code, and it produced a RTE for the case of [1,2,3] as well. Looking in your code for this case, you have:

temp=root->right;
root->right=root->left;
myflatten(root->right,nullptr);
myflatten(root->right,temp);

Maybe you forgot to set root->left to null. In this case, root->right and root->left point to the same node. This somehow produces a RTE instead of a wrong ans. Not sure why

• thanks for your analysis, it's very kind of you to answer my question so detailedly

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