merge-nodes-between-zero.js

/*

You are given the head of a linked list, which contains a series of integers separated by 0's. The beginning and end of the linked list will have Node.val == 0.

For every two consecutive 0's, merge all the nodes lying in between them into a single node whose value is the sum of all the merged nodes. The modified list should not contain any 0's.

Return the head of the modified linked list.

 

Example 1:

Input: head = [0,3,1,0,4,5,2,0]
Output: [4,11]
Explanation: 
The above figure represents the given linked list. The modified list contains
- The sum of the nodes marked in green: 3 + 1 = 4.
- The sum of the nodes marked in red: 4 + 5 + 2 = 11.

Example 2:

Input: head = [0,1,0,3,0,2,2,0]
Output: [1,3,4]
Explanation: 
The above figure represents the given linked list. The modified list contains
- The sum of the nodes marked in green: 1 = 1.
- The sum of the nodes marked in red: 3 = 3.
- The sum of the nodes marked in yellow: 2 + 2 = 4.


*/

var mergeNodes = function(head) {
    let p1 = head
    let zeroCounter = 0
    let sum = 0
    let newList = new ListNode(-1)
    let list = newList

    while(p1){

        sum += p1.val

        if(p1.val === 0){
            zeroCounter += 1
        }
        if(p1.val === 0 && zeroCounter === 2){
            list.next = new ListNode(sum)
            list = list.next
            sum = 0
            zeroCounter = 1
        }

        p1 = p1.next

    }

    return newList.next

};

/*
Instead of using two pointers I decided to use one pointer whick keeps track of how many times the 0 occurs 
*/