#20: add solution for exercise #2 in rust

rust/linked-lists/0002-add-two-numbers.rs

@@ -0,0 +1,45 @@
+// 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
+//     }
+//   }
+// }
+impl Solution {
+    pub fn add_two_numbers(l1: Option<Box<ListNode>>, l2: Option<Box<ListNode>>) -> Option<Box<ListNode>> {
+        fn add_lists(l1: Option<Box<ListNode>>, l2: Option<Box<ListNode>>, carry: i32) -> Option<Box<ListNode>> {
+            if l1.is_none() && l2.is_none() && carry == 0 {
+                return None;
+            }
+
+            let mut val = carry;
+            val += l1.as_ref().map(|l| l.val).unwrap_or(0);
+            val += l2.as_ref().map(|l| l.val).unwrap_or(0);
+
+            let mut result = ListNode::new(val%10);
+
+            if l1.is_some() || l2.is_some() {
+                let nxt = add_lists(
+                    l1.and_then(|l| l.next),
+                    l2.and_then(|l| l.next),
+                    if val > 9 {1} else {0}
+                );
+
+                result.next = nxt;
+            }
+
+            Some(Box::new(result))
+        }
+
+        add_lists(l1, l2, 0)
+    }
+}