Implemented p23 with 2 different solutions

src/p23_merge_k_sorted_lists.rs

@@ -1,11 +1,24 @@
-use super::linked_list::ListNode;
+pub mod sorted_vec {
+    use crate::linked_list::ListNode;
     
     pub struct Solution;
     impl Solution {
-    // TODO: implement
         pub fn merge_k_lists(lists: Vec<Option<Box<ListNode>>>) -> Option<Box<ListNode>> {
-        
+            let mut nums = vec![];
-        return None;
+            for mut list in lists {
+                while let Some(node) = list {
+                    nums.push(node.val);
+                    list = node.next;
+                }
+            }
+            nums.sort();
+            let mut head = None;
+            let mut tail = &mut head;
+            for num in nums {
+                *tail = Some(Box::new(ListNode::new(num)));
+                tail = &mut tail.as_mut().unwrap().next;
+            }
+            return head;
         }
     }
 
@@ -25,3 +38,53 @@ fn test2() {
     fn test3() {
         assert_eq!(Solution::merge_k_lists(vec![list![]]), list![]);
     }
+}
+
+pub mod binary_heap {
+    use crate::linked_list::ListNode;
+    use std::{collections::BinaryHeap, cmp::{Ordering, Reverse}};
+
+    pub struct Solution;
+    impl Solution {
+        pub fn merge_k_lists(lists: Vec<Option<Box<ListNode>>>) -> Option<Box<ListNode>> {
+            let mut lists = lists.into_iter()
+                .filter(Option::is_some)
+                .map(Reverse)
+                .collect::<BinaryHeap<_>>();
+            let mut head = None;
+            let mut tail = &mut head;
+            while let Some(Reverse(mut list)) = lists.pop() {
+                let next = list.as_mut().unwrap().next.take();
+                *tail = list;
+                tail = &mut tail.as_mut().unwrap().next;
+                if next.is_some() { lists.push(Reverse(next)); }
+            }
+            return head;
+        }
+    }
+
+    impl PartialOrd for ListNode {
+        fn partial_cmp(&self, other: &Self) -> Option<Ordering> { Some(self.cmp(other)) }
+    }
+
+    impl Ord for ListNode {
+        fn cmp(&self, other: &Self) -> Ordering { self.val.cmp(&other.val) }
+    }
+
+    #[test]
+    fn test1() {
+        assert_eq!(Solution::merge_k_lists(vec![
+            list![1,4,5], list![1,3,4], list![2,6]
+        ]), list![1,1,2,3,4,4,5,6]);
+    }
+
+    #[test]
+    fn test2() {
+        assert_eq!(Solution::merge_k_lists(vec![]), list![]);
+    }
+
+    #[test]
+    fn test3() {
+        assert_eq!(Solution::merge_k_lists(vec![list![]]), list![]);
+    }
+}