L6. Odd Even Linked List | Multiple Approaches

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[edisane]

Great video just a small correction that it will be
even = even.next
Here's the full code for leetcode:
ListNode* oddEvenList(ListNode* head) {
if(head == NULL || head->next == NULL) return head;

ListNode* odd = head;
ListNode* even = head->next;
ListNode* evenHead = head->next;

while(even!=NULL && even->next!=NULL){
odd->next = odd->next->next;
even->next = even->next->next;

odd = odd->next;
even = even->next;
}

odd->next = evenHead;
return head;
}

[mdtanveeransari]

if anyone is facing any issue with the while condition ie,
while(even != NULL && even -> next != NULL)
you can use instead,
while(odd -> next != NULL && even -> next != NULL)
i hope it helps you, happy coding.

[CodeNinja]

one mistake
even = even->next instead of even=even->next->next

[champ-kxlb]

well explained!
There is slight error in the brute force code that in while loop at the last line in loop even=even.next; so if anyone find its confusing can be helped from this.

[NotNewton]

hey guys, in the optimal solution, inside while loop, we have already set the next for both even and odd, so to go next even and odd use even= even->next ; odd= odd->next respectively
I spend my 20-30 minutes realising this lol :)

[pushankarmakar]

O(n/2) space complexity.

i was wrong. it'll be O(n) because we need to consider the operations taking place twice inside the array

[lovetiwadiai]

i think even next should also be even.next rather than even.next.next

[chetandatta]

Why is the time complexity O(n/2) * 2? It should be O(n/2) regardless of the number of operations performed inside the loop, right?

[shashamnk]

We would need to check if head !=null before initializing even as head.next and while updating even, even.next should be good enough, even.next.next would land us on an odd node.

[bhashasinha]

this is the java code
*
*
class Solution {
public ListNode oddEvenList(ListNode head) {
if(head==null ||head.next==null){
return head;
}
ListNode odd=head;
ListNode even=head.next;
ListNode connector=head.next;
while(even!=null && even.next!=null){
odd.next=odd.next.next;
even.next=even.next.next;

odd=odd.next;
even=even.next;
}
odd.next=connector;
return head;
}

[AmanSharma-xyqm]

All the video lectures and the articles helped me a lot to gain confidence in DSA and will be helping me in the interviews. Thank you Striver bhaiya for bringing such amazing content for free.

[ketonesgaming]

line even = even.next.next; inside the while loop. When updating the even pointer, you should check if even.next is not null before trying to access even.next.next. Small correction to be made

[rajmohitkumar]

Here is the java program
class Solution {
public ListNode oddEvenList(ListNode head) {
//edge case
if(head==null || head.next==null) return head;
ListNode odd=head;
ListNode even=head.next;
ListNode evenHead=head.next;
while(even !=null && even.next!=null){
odd.next=odd.next.next;
even.next=even.next.next;
odd=odd.next;
even=even.next;
}
odd.next=evenHead;
return head;

}
}

[abhinavprabhat]

LC 328.

// Naive solution
class Solution {
public:
ListNode* oddEvenList(ListNode* head) {
// naive solution is using a list to store the data

vector<int> arr;
ListNode* temp = head;

if(head ==NULL || head->next == NULL ) return head;
while(temp!=NULL && temp->next!=NULL){
arr.push_back(temp->val);
temp = temp->next->next;
}
if(temp) arr.push_back(temp->val);

temp = head->next;
while(temp!=NULL && temp->next!=NULL){
arr.push_back(temp->val);
temp = temp->next->next;
}
if(temp) arr.push_back(temp->val);

int i =0; temp = head;
while(temp!=NULL){
temp->val = arr[i];
i++;
temp = temp->next;
}

return head;

}
};

// optimised solution

class Solution {
public:

ListNode* oddEvenList(ListNode* head) {


if(head == NULL || head->next == NULL ) return head;
ListNode* oddptr = head;
ListNode* evenptr = head->next;
ListNode* evenhead = head->next;

while(evenptr !=NULL && evenptr->next!=NULL){
oddptr->next = oddptr->next->next;
evenptr->next = evenptr->next->next;

oddptr = oddptr->next;
evenptr= evenptr->next;
}

oddptr->next = evenhead;

return head;
}
};

[manishmahajan]

Marking my Day 21 of learning DSA. Thanks for the great course with clear in-depth explanation

[BhavyaJain-qzjg]

solved without watching, kudos to previous videos base creation !!

[Sawlf]

Why did the brute force seemed more complex than the optimized 💀

[mdtanveeransari]

we need the article for rest of the linked list problems of A2Z sheet

[amangoyal]

i can surely say that this is the best linkedList course of all time

[nitishkumarram]

0(n)time complexity, understood thank you striver bhaiya