LeetCode 2181: Merge Nodes in Between Zeros Solution

Master LeetCode problem 2181 (Merge Nodes in Between Zeros), a medium challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

2181. Merge Nodes in Between Zeros

Medium

Linked List Simulation

Problem Explanation

Explanation

To solve this problem, we can iterate over the linked list and whenever we encounter two consecutive zeros, we merge all the nodes between them by calculating the sum of their values. We update the pointers accordingly to skip the merged nodes. We continue this process until we reach the end of the linked list.

Time complexity: O(n), where n is the number of nodes in the linked list.
Space complexity: O(1) since we are modifying the original linked list in place.

Solution Code

class ListNode {
    int val;
    ListNode next;
    
    ListNode(int val) {
        this.val = val;
    }
}

public ListNode mergeNodesInBetweenZeros(ListNode head) {
    ListNode dummy = new ListNode(0);
    dummy.next = head;
    ListNode prev = dummy;
    
    while (prev != null && prev.next != null) {
        ListNode start = prev.next;
        ListNode end = start;
        int sum = 0;
        
        while (end != null && end.val != 0) {
            sum += end.val;
            end = end.next;
        }
        
        if (end != null && end.next != null && end.next.val == 0) {
            prev.next = new ListNode(sum);
            prev.next.next = end.next.next;
        }
        
        prev = prev.next;
    }
    
    return dummy.next;
}

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