The correct, optimal and working solution for programming question insert-head-ll on hackerrank

/* * Author: Arpit Bhayani * https://arpitbhayani.me */ #include <cmath> #include <cstdio> #include <cstdlib> #include <climits> #include <deque> #include <iostream> #include <list> #include <limits> #include <map> #include <queue> #include <set> #include <stack> #include <vector> #define ll long long #define MIN(a, b) a < b ? a : b #define MAX(a, b) a > b ? a : b using namespace std; int readline(char *str) { int i = 0; char ch; while((ch = getchar()) != '\n') { str[i++] = ch; } str[i] = '\0'; return i; } struct Node { int data; struct Node *next; }; struct Node * new_node(int v) { struct Node * p = (struct Node *) calloc(1, sizeof(struct Node)); p->data = v; return p; } struct Node * Insert(struct Node *head, int data) { struct Node * p = head; if(p == NULL) { return new_node(data); } struct Node * t = new_node(data); t->next = head; return t; } int main(int argc, char *argv[]) { struct Node * head = new_node(1); head->next = new_node(2); Insert(head, 3); return 0; }