Merge pull request #2943 from master-of-none/problem25

Create: 0025-reverse-nodes-in-k-group.rs

Author: felivalencia3

Diff for: rust/0025-reverse-nodes-in-k-group.rs

@@ -0,0 +1,48 @@
+impl Solution {
+    pub fn reverse_k_group(head: Option<Box<ListNode>>, k: i32) -> Option<Box<ListNode>> {
+        let mut dummy = Some(Box::new(ListNode {next: head, val: 0 }));
+        let mut cur = dummy.as_mut();
+
+        'outer: loop {
+            let mut start = cur.as_mut().unwrap().next.take();
+            if start.is_none() {
+                break 'outer;
+            }
+
+            let mut end = start.as_mut();
+            for _ in 0..(k - 1) {
+                end = end.unwrap().next.as_mut();
+
+                if end.is_none() {
+                    cur.as_mut().unwrap().next = start;
+                    break 'outer;
+                }
+            }
+
+            let mut tail = end.as_mut().unwrap().next.take();
+            let end = Solution::reverse(start, tail);
+            cur.as_mut().unwrap().next = end;
+
+            for _ in 0..k {
+                cur = cur.unwrap().next.as_mut()
+            }
+        }
+        dummy.unwrap().next
+    }
+
+    fn reverse(
+        mut head: Option<Box<ListNode>>,
+        tail: Option<Box<ListNode>>,
+    ) -> Option<Box<ListNode>> {
+        let mut prev = tail;
+        let mut cur = head;
+
+        while let Some(mut cur_node) = cur {
+            let mut next = cur_node.next.take();
+            cur_node.next = prev.take();
+            prev = Some(cur_node);
+            cur = next
+        }
+        prev
+    }
+}