Merge nodes in between zeros

Linked List Simulation

89.7% acceptance

Feb 23, 2026

2494

You are given the head of a linked list with series of integers separated by 0's. The beginning and end of the list have Node.val == 0. For every two consecutive 0's, merge all nodes between them into a single node whose value is the sum of all merged nodes. Return the head of the modified list.

Solution

Rust

Time O(n)

Space O(n)

LeetCode

solution.rs

impl Solution {
  pub fn merge_nodes(head: Option<Box<ListNode>>) -> Option<Box<ListNode>> {
    let mut values = Vec::new();
    let mut cur = head;
    let mut sum = 0i32;
    // Skip the leading 0
    cur = cur?.next;
    while let Some(node) = cur {
      if node.val == 0 {
        values.push(sum);
        sum = 0;
      } else {
        sum += node.val;
      }
      cur = node.next;
    }
    // Build result list
    let mut dummy = Box::new(ListNode::new(0));
    let mut tail = &mut dummy;
    for v in values {
      tail.next = Some(Box::new(ListNode::new(v)));
      tail = tail.next.as_mut().unwrap();
    }
    dummy.next
  }
}