leetcode/rust/0002-add-two-numbers.rs at main · neetcode-gh/leetcode · GitHub

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impl Solution {
    pub fn add_two_numbers(l1: Option<Box<ListNode>>, l2: Option<Box<ListNode>>) -> Option<Box<ListNode>> {
        let (mut l1, mut l2) = (l1.as_ref(), l2.as_ref());
        let mut dummy = Box::new(ListNode { val: 0, next: None });
        let mut cur = dummy.as_mut();
        let mut carry = 0;

        while l1.is_some() || l2.is_some() || carry > 0 {
            let val1 = l1.map(|n| n.val).unwrap_or_default();
            let val2 = l2.map(|n| n.val).unwrap_or_default();

            let sum = val1 + val2 + carry;
            carry = sum / 10;
            cur.next = Some(Box::new(ListNode { val: sum % 10, next:  None }));
            cur = cur.next.as_mut().unwrap();

            if let Some(node) = l1 { l1 = node.next.as_ref() }
            if let Some(node) = l2 { l2 = node.next.as_ref() }
        }

        dummy.next
    }
}