Merge Nodes in Between Zeros

class Solution {
public:
    ListNode* mergeLinkedList(ListNode* start) {
        // Moving to first non-zero node
        start = start->next;
        if (start == nullptr) {
            return start;
        }

        // Temporary pointer setup
        ListNode* current = start;
        int total = 0;
        while (current->val != 0) {
            total += current->val;
            current = current->next;
        }

        // Assign the accumulated total to start node
        start->val = total;
        // Recursively process the remaining list
        start->next = mergeLinkedList(current);
        return start;
    }
};

The given C++ code defines a function within a class named Solution that merges nodes in a linked list between zeros. The main purpose of this function, mergeLinkedList, is to create a new linked list where each segment of nodes enclosed by zeros is merged into a single node representing the sum of those nodes.

Follow these steps to understand the operation of this function:

1. Start by moving to the first non-zero node. This skips the initial zero in the list.
2. Check if the node is null. If so, return null, as there are no further nodes to process.
3. Initialize a temporary pointer, current, that will traverse through the list starting from the first non-zero node.
4. Use a variable total to accumulate the values of the nodes until the next zero is reached.
5. Iterate through the list, adding the value of current to total until a node with value zero is found.
6. Assign the accumulated total to the value of the start node.
7. Recursively call mergeLinkedList with the next segment of the list starting from the zero node found.
8. The function returns the modified list starting from start, which now contains the merged values between zeros.

By applying this recursive approach, all nodes between zeros are effectively merged by summing their values and resetting pointers to skip over nodes till the next zero is reached, hence transforming the list as required.

class Solution {

    public ListNode combineNodes(ListNode startNode) {
        // Move to the first relevant node
        startNode = startNode.next;
        if (startNode == null) {
            return startNode;
        }

        // Prepare for processing
        ListNode current = startNode;
        int total = 0;
        while (current.val != 0) {
            total += current.val;
            current = current.next;
        }

        // Assign the computed total to the starting node's value
        startNode.val = total;
        // Continue merging with the rest of the list
        startNode.next = combineNodes(current);
        return startNode;
    }
}

This Java solution addresses the problem of merging nodes in a linked list between zero-valued nodes. Specifically, the solution involves a recursive function combineNodes that processes segments of the linked list separated by zeros.

• Create a method combineNodes that takes a ListNode startNode as its parameter. This method is designed to merge consecutive nodes in a linked list that lie between nodes having a value of zero.

• Each invocation of combineNodes starts by skipping the initial zero node and moving to the first node that will contribute to the sum.

• Initialize an integer total to accumulate the sum of node values in the current segment, starting from startNode until another zero node is encountered.

• Iterate through the nodes, adding up their values until a node with the value zero is found. During this process, use a pointer current to traverse the list.

• Once a zero is reached (which indicates the end of a segment), assign the computed total to the value of startNode. This effectively merges all values between the two zero nodes into the starting node of the segment.

• Recursively call combineNodes on the node following the zero to process the next segment.

• The method returns the modified startNode, which now represents the merged value of the segment, and its next pointer is set to the result of the recursive call.

This approach neatly handles merging of nodes section by section, utilizing recursion to continue processing until the end of the list. By updating only the starting nodes of each segment, it minimizes changes to the original list structure, ensuring efficient in-place updating of node values.

class Solution:
    def mergeNodes(self, starting_node):
        # Move to the initial non-zero node.
        starting_node = starting_node.next
        if not starting_node:
            return starting_node

        # Setup a temporary node for traversal.
        current_node = starting_node
        total = 0
        while current_node.val != 0:
            total += current_node.val
            current_node = current_node.next

        # Assign the computed total to starting_node's value.
        starting_node.val = total
        # Link to the next processed node via recursion.
        starting_node.next = self.mergeNodes(current_node)
        return starting_node

The solution provided in Python involves a recursive approach for merging nodes in a linked list based on specified conditions. Here's the summary:

• Initialize by moving to the first non-zero node in the linked list.
• Once the first non-zero node is identified, start the process of aggregation:
  • Traverse the nodes, adding up their values until another zero node is encountered.
  • This aggregation is stored in a variable total.
• After completing the summation up to the next zero node:
  • Assign the total sum to the value of the current starting node.
  • Use recursion to handle the rest of the list starting from the next zero node.
  • The recursion continues until the end of the list is reached, effectively processing and linking all segments between zeros.
• Return the modified list from the starting node.

This solution modifies the original linked list and uses recursion to manage and merge sets of nodes between zeros efficiently.