how to avoid same input id value in c++ - c++

Question

how to avoid double id in linked listed, example, i have id, name, gol, so firtst, i input id= 12, name=jon gol=A, when i input again. id=12, its show message "Id cant be same". input again can you help
this is my code for insert linked list first node,
#include <iostream>
#include <string>
#include <conio.h>
struct node {
int id;
char name[20], gol;
node *next;
};
node *head = nullptr;
node *tail = nullptr;
void tambah_awal_list() {
int id;
char name[20];
char gol;
node *baru = new node;
baru->id=head->id;
std::cout << "Id : ";
std::cin >> baru->id;
if (head->id == baru->id){
std::cout << "Id cant be same"<<std::endl;
}
std::cout << "Name : ";
std::cin >> baru->name;
std::cout << "Blood type (A/B/O) : ";
std::cin >> baru->gol;
if(head == nullptr) {
head = baru;
head->next = nullptr;
tail = head;
} else {
baru->next = head;
head = baru;
}
}
what should i change?

Answer 1

It depends on the spec and performance requirements.
If id could be decided by code instead of user input, then you just need to have an global counter increment every time a node is created.
You have to handle it carefully under multi-threading cases or very large number when number of nodes is out of range of int.
// Global variable or class member
int g_nextID = 0;
int generateID(){return ++g_nextID;}
void generate(){
node* n = new node();
n->id = generateID();
// ...
}
Use std::unordered_set<int> which takes O(1) time and O(N) space.
// A global variable or class member
std::unordered_set<int> g_used;
node *head = nullptr;
node *tail = nullptr;
void generate(){
// Inside the function
int id;
// Get user input into id
// ...
// Checking if used
if(g_used.find(id) == g_used.end()){
// Create the node
// ...
g_used.insert(id); // Save it
}else{
// Error handling.
}
}
void removeNode(int id){
// Remove it from list
// ...
// Remove it from set
g_used.erase(id);
}
Lookup the nodes, but it takes O(N) times.