Implemented p24, changed linked_list impotr to always use crate in its path instead of super, modified p19

src/lib.rs

@@ -23,3 +23,4 @@ pub mod p20_valid_parentheses;
 pub mod p21_merge_two_sorted_lists;
 pub mod p22_generate_parentheses;
 pub mod p23_merge_k_sorted_lists;
+pub mod p24_swap_nodes_in_pairs;

src/p19_remove_nth_node_from_end_of_list.rs

@@ -1,26 +1,24 @@
-use super::linked_list::ListNode;
+use crate::linked_list::ListNode;
 
 pub struct Solution;
 impl Solution {
     pub fn remove_nth_from_end(head: Option<Box<ListNode>>, n: i32) -> Option<Box<ListNode>> {
-        let mut head = head.unwrap();
+        let mut dummy = Some(Box::new(ListNode { val: 0, next: head }));
-        let mut node_before_nth: &mut Box<ListNode>;
+        let mut node_before_nth: &mut Option<Box<ListNode>>;
         // unsafe is required to have immutable and mutable references at the same time
-        // in order to avoid cloning the list altogether
+        // in order to avoid cloning the list
-        unsafe { node_before_nth = &mut *(&mut head as *mut Box<ListNode>); };
+        unsafe { node_before_nth = &mut *(&mut dummy as *mut Option<Box<ListNode>>); };
-        let mut tail = &head;
+        let mut tail = &dummy.as_ref().unwrap().next;
-        for _ in 0..n-1 {
+        for _ in 0..n {
-            tail = tail.next.as_ref().unwrap();
+            tail = &tail.as_ref().unwrap().next;
         }
-        if tail.next.is_none() { return head.next; }
+        while tail.is_some() {
-        else { tail = tail.next.as_ref().unwrap(); }
+            tail = &tail.as_ref().unwrap().next;
-        while tail.next.is_some() {
+            node_before_nth = &mut node_before_nth.as_mut().unwrap().next;
-            tail = tail.next.as_ref().unwrap();
-            node_before_nth = node_before_nth.next.as_mut().unwrap();
         }
-        let node_to_remove = node_before_nth.next.as_mut().unwrap();
+        let node_to_remove = &mut node_before_nth.as_mut().unwrap().next;
-        node_before_nth.next = node_to_remove.next.take();
+        node_before_nth.as_mut().unwrap().next = node_to_remove.as_mut().unwrap().next.take();
-        return Some(head);
+        return dummy.unwrap().next;
     }
 }
 

src/p24_swap_nodes_in_pairs.rs

@@ -0,0 +1,34 @@
+use crate::linked_list::ListNode;
+
+pub struct Solution;
+impl Solution {
+    pub fn swap_pairs(mut head: Option<Box<ListNode>>) -> Option<Box<ListNode>> {
+        if head.is_none() { return None; }
+        let mut tail = &mut head;
+        while tail.is_some() {
+            let next = &mut tail.as_mut().unwrap().next;
+            if next.is_none() { break; }
+            let mut next_node = next.take();
+            tail.as_mut().unwrap().next = next_node.as_mut().unwrap().next.take();
+            next_node.as_mut().unwrap().next = tail.take();
+            tail.replace(next_node.unwrap());
+            tail = &mut tail.as_mut().unwrap().next.as_mut().unwrap().next;
+        }
+        return head;
+    }
+}
+
+#[test]
+fn test1() {
+    assert_eq!(Solution::swap_pairs(list![1,2,3,4]), list![2,1,4,3]);
+}
+
+#[test]
+fn test2() {
+    assert_eq!(Solution::swap_pairs(list![]), list![]);
+}
+
+#[test]
+fn test3() {
+    assert_eq!(Solution::swap_pairs(list![1]), list![1]);
+}

src/p2_add_two_numbers.rs

@@ -1,4 +1,4 @@
-use super::linked_list::ListNode;
+use crate::linked_list::ListNode;
 
 pub struct Solution;
 impl Solution {