Add two numbers ii

Linked List Math Stack

62.4% acceptance

Jan 13, 2026

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You are given two non-empty linked lists representing two non-negative integers. The most significant digit comes first and each of their nodes contains a single digit. Add the two numbers and return the sum as a linked list. You may assume the two numbers do not contain any leading zero, except the number 0 itself.

Solution

Rust

Time O(n)

Space O(n)

LeetCode

solution.rs

impl Solution {
  pub fn add_two_numbers(l1: Option<Box<ListNode>>, l2: Option<Box<ListNode>>) -> Option<Box<ListNode>> {
    let mut stack1 = Vec::new();
    let mut stack2 = Vec::new();
    
    let mut curr = l1;
    while let Some(node) = curr {
      stack1.push(node.val);
      curr = node.next;
    }
    
    let mut curr = l2;
    while let Some(node) = curr {
      stack2.push(node.val);
      curr = node.next;
    }
    
    let mut result = None;
    let mut carry = 0;
    
    while !stack1.is_empty() || !stack2.is_empty() || carry > 0 {
      let v1 = stack1.pop().unwrap_or(0);
      let v2 = stack2.pop().unwrap_or(0);
      let sum = v1 + v2 + carry;
      carry = sum / 10;
      
      let mut node = ListNode::new(sum % 10);
      node.next = result;
      result = Some(Box::new(node));
    }
    
    result
  }
}