The correct, optimal and working solution for programming question reverse-dll 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 *prev; }; void Print(struct Node *head) { struct Node *p = head; while(p) { printf("%d\n", p->data); p = p->next; } } struct Node * new_node(int v) { struct Node * p = (struct Node *) calloc(1, sizeof(struct Node)); p->data = v; return p; } struct Node * SortedInsert(struct Node * head, int data) { struct Node * p = head; struct Node * t = new_node(data); if(head == NULL) { return t; } while(p->next && p->data <= data) { p = p->next; } if(p == head && data < p->data) { t->next= head; head->prev = t; return t; } if(p->next == NULL && p->data < data) { t->prev = p; p->next = t; } else { t->next = p; t->prev = p->prev; p->prev->next = t; p->prev = t; } return head; } struct Node * Reverse(struct Node * head) { struct Node * p = head; struct Node * prev = NULL; while(p) { struct Node * t; t = p->next; p->next = p->prev; p->prev = t; prev = p; p = p->prev; } return prev; } int main(int argc, char *argv[]) { struct Node * head = NULL; head = SortedInsert(head, 1); head = SortedInsert(head, 4); head = SortedInsert(head, 2); head = SortedInsert(head, 3); head = SortedInsert(head, 7); head = SortedInsert(head, 6); head = SortedInsert(head, 9); head = SortedInsert(head, 10); Print(head); head = Reverse(head); Print(head); return 0; }