add initial data

add-two-numbers/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "add-two-numbers"
+version = "0.1.0"

add-two-numbers/Cargo.toml

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+[package]
+name = "add-two-numbers"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]

add-two-numbers/src/main.rs

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+fn main() {
+    let l1 = to_nodes(942);
+    let l2 = to_nodes(9465);
+    let result = *add_two_numbers(l1, l2).unwrap();
+    dbg!(result);
+}
+
+fn add_two_numbers(l1: Option<Box<ListNode>>, l2: Option<Box<ListNode>>) -> Option<Box<ListNode>> {
+    let mut l1 = l1;
+    let mut l2 = l2;
+
+    let mut carry = false;
+    let mut head = None;
+    let mut tail = &mut head;
+
+    while l1.is_some() || l2.is_some() || carry {
+        let a = l1.as_ref().map_or(0, |n| n.val);
+        let b = l2.as_ref().map_or(0, |n| n.val);
+
+        let addition = a + b + carry as i32;
+
+        let node = Box::new(ListNode::new(addition % 10));
+        carry = addition >= 10;
+
+        *tail = Some(node);
+        tail = &mut tail.as_mut().unwrap().next;
+
+        l1 = l1.and_then(|n| n.next);
+        l2 = l2.and_then(|n| n.next);
+    }
+
+    head
+}
+
+/////////////////////////////
+
+// Definition for singly-linked list.
+#[derive(PartialEq, Eq, Clone, Debug)]
+pub struct ListNode {
+    pub val: i32,
+    pub next: Option<Box<ListNode>>,
+}
+
+impl ListNode {
+    #[inline]
+    fn new(val: i32) -> Self {
+        ListNode { next: None, val }
+    }
+}
+
+////////////////////////////////
+
+fn to_nodes(number: i32) -> Option<Box<ListNode>> {
+    let digits = number
+        .to_string()
+        .chars()
+        .map(|c| c.to_string().parse().unwrap())
+        .rev()
+        .collect::<Vec<i32>>();
+
+    let mut node = ListNode::new(digits[0]);
+
+    for item in digits.iter().skip(1) {
+        push(&mut node, *item);
+    }
+
+    Some(Box::new(node))
+}
+
+fn push(node: &mut ListNode, digit: i32) {
+    if node.next.is_some() {
+        push(node.next.as_mut().unwrap(), digit);
+    } else {
+        let new = ListNode::new(digit);
+        node.next = Some(Box::new(new));
+    }
+}