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OddEvenLinkedList.java
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OddEvenLinkedList.java
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package com.leetcode;
public class OddEvenLinkedList {
// https://leetcode.com/problems/odd-even-linked-list/
// here we are talking about the node number and not the value in the nodes.
class Solution {
public ListNode oddEvenList(ListNode head) {
if(head == null || head.next == null) return head;
ListNode list1 = head;//odd head
ListNode list2 = head.next;//even head
ListNode odd;
ListNode even;
odd = head;
even = odd.next;
while(odd != null && even != null){
odd.next = even.next;
if(odd.next == null) break;
odd = odd.next;
even.next = odd.next;
if(even.next == null) break;
even = even.next;
}
odd.next = list2;
return head;//odd head
}
}
/**
* Definition for singly-linked list.
*/
public class ListNode {
int val;
ListNode next;
ListNode() {}
ListNode(int val) { this.val = val; }
ListNode(int val, ListNode next) { this.val = val; this.next = next; }
}
//Compressed
public class Solution2 {
public ListNode oddEvenList(ListNode head) {
if (head == null) return null;
ListNode odd = head, even = head.next, evenHead = even;
while (even != null && even.next != null) {//better check even and even.next as it comes always after odd
odd.next = even.next;
odd = odd.next;
even.next = odd.next;
even = even.next;
}
odd.next = evenHead;
return head;
}
}
}