Check if subtree

Given two binary trees with head reference as T and S having at most N nodes. The task is to check if S is present as subtree in T.

A subtree of a tree T1 is a tree T2 consisting of a node in T1 and all of its descendants in T1.

• Time : O(n)
• Space : O(1)

class Solution
{
    bool helper(Node* a, Node* b) {
        if(!a and !b) return true;
        if(!a or !b) return false;
        if(a->data != b->data) return false;
        return helper(a->left, b->left) and helper(a->right, b->right);
    }
  public:
    //Function to check if S is a subtree of tree T.
    bool isSubTree(Node* T, Node* S) 
    {
        if(!T) return false;
        if(helper(T, S)) return true;
        return isSubTree(T->left, S) or isSubTree(T->right, S);
    }
};