Merge pull request #2637 from rmrt1n/023

Create 0023-merge-k-sorted-lists.rs

rust/0023-merge-k-sorted-lists.rs

@@ -0,0 +1,44 @@
+impl Solution {
+    pub fn merge_k_lists(lists: Vec<Option<Box<ListNode>>>) -> Option<Box<ListNode>> {
+        fn merge(list1: Option<Box<ListNode>>, list2: Option<Box<ListNode>>) -> Option<Box<ListNode>> {
+            match (list1, list2) {
+                (None, None) => None,
+                (None, Some(l)) | (Some(l), None) => Some(l),
+                (Some(l1), Some(l2)) => {
+                    if l1.val < l2.val {
+                        return Some(Box::new(ListNode {
+                            val: l1.val,
+                            next: merge(l1.next, Some(l2)),
+                        }));
+                    }
+                    Some(Box::new(ListNode {
+                        val: l2.val,
+                        next: merge(Some(l1), l2.next),
+                    }))
+                }
+            }
+        }
+
+        if lists.is_empty() {
+            return None;
+        }
+
+        let mut lists = lists;
+
+        while lists.len() > 1 {
+            let mut merged = vec![];
+            for i in (0..lists.len()).step_by(2) {
+                let l1 = lists[i].take();
+                let l2 = if i + 1 < lists.len() {
+                    lists[i + 1].take()
+                } else {
+                    None
+                };
+                merged.push(merge(l1, l2))
+            }
+            lists = merged;
+        }
+
+        lists[0].take()
+    }
+}