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This approach involves traversing the linked list using a single pass while keeping a temporary sum of node values between consecutive zeros. We use a dummy node to help simplify edge cases related to list modifications.
Time Complexity: O(n), where n is the number of nodes in the linked list as we traverse the list only once.
Space Complexity: O(1), excluding the space needed for the new output list.
1function ListNode(val, next) {
2 this.val = (val===undefined ? 0 : val)
3 this.next = (next===undefined ? null : next)
4}
5
6function mergeNodes(head) {
7 let dummy = new ListNode(0);
8 let tail = dummy;
9 let sum = 0;
10 let current = head.next; // Skip the leading zero
11
12 while (current) {
13 if (current.val === 0) {
14 tail.next = new ListNode(sum);
15 tail = tail.next;
16 sum = 0;
17 } else {
18 sum += current.val;
19 }
20 current = current.next;
21 }
22
23 return dummy.next;
24}The JavaScript solution constructs a new linked list using a dummy node. Each segment sum is inserted as a new node by traversing nodes between zeros.
Another approach we can take involves recursion to solve each segment between the zeros sequentially. Though iterative is usually preferred for this problem, recursion can offer a more functional programming perspective.
Time Complexity: O(n)
Space Complexity: O(n) due to recursive stack space
1 public int val;
public ListNode next;
public ListNode(int val=0, ListNode next=null) {
this.val = val;
this.next = next;
}
}
public class Solution {
private void RecursiveMerge(ListNode node, ref int sum, ref ListNode last) {
if (node == null) return;
if (node.val == 0 && sum > 0) {
last.next = new ListNode(sum);
last = last.next;
sum = 0;
} else if (node.val != 0) {
sum += node.val;
}
RecursiveMerge(node.next, ref sum, ref last);
}
public ListNode MergeNodes(ListNode head) {
ListNode dummy = new ListNode(0);
ListNode last = dummy;
int sum = 0;
RecursiveMerge(head.next, ref sum, ref last);
return dummy.next;
}
}This C# solution uses recursion to accumulate node values between zeros. Using references allows persistence of sums and node additions throughout recursive calls.