The correct, optimal and working solution for programming question odd-even-linked-list on leetcode

/* * 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 val; struct node * next; }; struct node * new_node(int d) { struct node * t = (struct node *) calloc(1, sizeof(struct node)); t->val = d; return t; } void printList(struct node * head) { struct node * p = head; while(p) { printf("%d ", p->val); p = p->next; } printf("\n"); } struct node * oddEvenList(struct node * head) { if(head == NULL) { return NULL; } struct node * odd_head = NULL, * even_head = NULL; struct node * odd_tail = NULL, * even_tail = NULL; struct node * odd_tail_prev = NULL; odd_head = odd_tail = head; even_head = even_tail = head->next; while(odd_tail && even_tail) { if(odd_tail->next) { odd_tail->next = odd_tail->next->next; } if(even_tail->next) { even_tail->next = even_tail->next->next; } odd_tail_prev = odd_tail; odd_tail = odd_tail->next; even_tail = even_tail->next; } if(odd_tail) { odd_tail->next = even_head; } else { odd_tail_prev->next = even_head; } return odd_head; } int main(int argc, char *argv[]) { struct node * head = new_node(1); head->next = new_node(2); head->next->next = new_node(3); head->next->next->next = new_node(4); head->next->next->next->next = new_node(5); head->next->next->next->next->next = new_node(6); head = oddEvenList(head); printList(head); return 0; }