LEETCODE-Linked-List-2181

The provided code snippet for the mergeNodes method is intended to solve a specific problem involving a linked list. However, there seem to be a couple of issues in the logic. Let me first explain the problem this code aims to solve, then correct and optimize the logic.

Code

Here’s a corrected and optimized version of the code:

class ListNode {
  int val;
  ListNode next;
  ListNode(int x) { val = x; }
}

class Solution {
  public ListNode mergeNodes(ListNode head) {
    ListNode dummy = new ListNode(0);
    ListNode tail = dummy;
    ListNode current = head.next; // Start after the initial zero

    int sum = 0;

    while (current != null) {
      if (current.val == 0) {
        tail.next = new ListNode(sum);
        tail = tail.next;
        sum = 0;
      } else {
        sum += current.val;
      }
      current = current.next;
    }

    return dummy.next;
  }
}

Explanation

1. Initialization:

   • A dummy node (dummy) is created to simplify the construction of the result list.
   • A tail pointer is used to keep track of the end of the result list.
   • The current pointer starts from the node after the initial zero (as the problem implies that every segment starts with a zero).

2. Iteration and Summation:

   • Iterate through the list, summing values between zeros.
   • When a zero is encountered, add a new node with the sum to the result list and reset the sum.

3. Returning the Result:

   • The dummy.next points to the head of the merged list, which is returned as the final result.

This corrected implementation should handle the merging of nodes between zeros as expected.