This function returns true if there is pair in DLL with sum equal to given sum . The algorithm is similar to hasArrayTwoCandidates ( ) tinyurl . com / dy6palr in method 1 of http :
bool isPresentInDLL ( node * head , node * tail , int sum ) { while ( head != tail ) { int curr = head -> key + tail -> key ; if ( curr == sum ) return true ; else if ( curr > sum ) tail = tail -> left ; else head = head -> right ; } return false ; }