From e798e5acdee69416d61c8ab65cea4da8a5c16355 Mon Sep 17 00:00:00 2001
From: Bama Charan Chhandogi <b.c.chhandogi@gmail.com>
Date: Mon, 2 Oct 2023 05:49:39 +0530
Subject: [PATCH] add reverse k group linkedlist (#9323)

* add reverse k group linkedlist

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* update

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* Update reverse_k_group.py

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* Update reverse_k_group.py

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* Update reverse_k_group.py

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Christian Clauss <cclauss@me.com>
---
 .../linked_list/reverse_k_group.py            | 118 ++++++++++++++++++
 1 file changed, 118 insertions(+)
 create mode 100644 data_structures/linked_list/reverse_k_group.py

diff --git a/data_structures/linked_list/reverse_k_group.py b/data_structures/linked_list/reverse_k_group.py
new file mode 100644
index 000000000000..5fc45491a540
--- /dev/null
+++ b/data_structures/linked_list/reverse_k_group.py
@@ -0,0 +1,118 @@
+from __future__ import annotations
+
+from collections.abc import Iterable, Iterator
+from dataclasses import dataclass
+
+
+@dataclass
+class Node:
+    data: int
+    next_node: Node | None = None
+
+
+class LinkedList:
+    def __init__(self, ints: Iterable[int]) -> None:
+        self.head: Node | None = None
+        for i in ints:
+            self.append(i)
+
+    def __iter__(self) -> Iterator[int]:
+        """
+        >>> ints = []
+        >>> list(LinkedList(ints)) == ints
+        True
+        >>> ints = tuple(range(5))
+        >>> tuple(LinkedList(ints)) == ints
+        True
+        """
+        node = self.head
+        while node:
+            yield node.data
+            node = node.next_node
+
+    def __len__(self) -> int:
+        """
+        >>> for i in range(3):
+        ...     len(LinkedList(range(i))) == i
+        True
+        True
+        True
+        >>> len(LinkedList("abcdefgh"))
+        8
+        """
+        return sum(1 for _ in self)
+
+    def __str__(self) -> str:
+        """
+        >>> str(LinkedList([]))
+        ''
+        >>> str(LinkedList(range(5)))
+        '0 -> 1 -> 2 -> 3 -> 4'
+        """
+        return " -> ".join([str(node) for node in self])
+
+    def append(self, data: int) -> None:
+        """
+        >>> ll = LinkedList([1, 2])
+        >>> tuple(ll)
+        (1, 2)
+        >>> ll.append(3)
+        >>> tuple(ll)
+        (1, 2, 3)
+        >>> ll.append(4)
+        >>> tuple(ll)
+        (1, 2, 3, 4)
+        >>> len(ll)
+        4
+        """
+        if not self.head:
+            self.head = Node(data)
+            return
+        node = self.head
+        while node.next_node:
+            node = node.next_node
+        node.next_node = Node(data)
+
+    def reverse_k_nodes(self, group_size: int) -> None:
+        """
+        reverse nodes within groups of size k
+        >>> ll = LinkedList([1, 2, 3, 4, 5])
+        >>> ll.reverse_k_nodes(2)
+        >>> tuple(ll)
+        (2, 1, 4, 3, 5)
+        >>> str(ll)
+        '2 -> 1 -> 4 -> 3 -> 5'
+        """
+        if self.head is None or self.head.next_node is None:
+            return
+
+        length = len(self)
+        dummy_head = Node(0)
+        dummy_head.next_node = self.head
+        previous_node = dummy_head
+
+        while length >= group_size:
+            current_node = previous_node.next_node
+            assert current_node
+            next_node = current_node.next_node
+            for _ in range(1, group_size):
+                assert next_node, current_node
+                current_node.next_node = next_node.next_node
+                assert previous_node
+                next_node.next_node = previous_node.next_node
+                previous_node.next_node = next_node
+                next_node = current_node.next_node
+            previous_node = current_node
+            length -= group_size
+        self.head = dummy_head.next_node
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()
+    ll = LinkedList([1, 2, 3, 4, 5])
+    print(f"Original Linked List: {ll}")
+    k = 2
+    ll.reverse_k_nodes(k)
+    print(f"After reversing groups of size {k}: {ll}")