Rotate a Linked LIst

Author: anantkaushik

Python/GeeksforGeeks/rotate-a-linked-list.py

@@ -0,0 +1,112 @@
+"""
+Problem Link: https://practice.geeksforgeeks.org/problems/rotate-a-linked-list/1
+
+Given a singly linked list of size N. The task is to rotate the linked list counter-clockwise by k nodes,
+where k is a given positive integer smaller than or equal to length of the linked list.
+
+Input Format:
+First line of input contains number of testcases T. For each testcase, first line of input contains length of 
+linked list and next line contains linked list elements and last line contains k, by which linked list is to be rotated.
+
+Output Format:
+For each testcase, print the rotated linked list.
+
+User Task:
+The task is to complete the function rotate() which takes head reference as the first argument and k as the second argument. 
+The printing is done automatically by the driver code.
+
+Constratints:
+1 <= T <= 100
+1 <= N <= 103
+1 <= k <= 103
+
+Example:
+Input:
+3
+8
+1 2 3 4 5 6 7 8
+4
+5
+2 4 7 8 9
+3
+2
+1 2
+4
+
+Output:
+5 6 7 8 1 2 3 4
+8 9 2 4 7
+1 2
+
+Explanation:
+Testcase 1: After rotating the linked list by 4 elements (anti-clockwise), we reached to node 5, which is (k+1)th node 
+from beginning, now becomes head and tail of the linked list is joined to the previous head.
+"""
+class Node:
+    def __init__(self, data):
+        self.data = data
+        self.next = None
+class LinkedList:
+    def __init__(self):
+        self.head = None
+    def push(self, new_data):
+        new_node = Node(new_data)
+        new_node.next = self.head
+        self.head = new_node
+    def printList(self):
+        temp = self.head
+        while(temp):
+            print(temp.data, end=" ")
+            # arr.append(str(temp.data))
+            temp = temp.next
+        print("")
+if __name__ == '__main__':
+    start = LinkedList()
+    t = int(input())
+    while(t > 0):
+        llist = LinkedList()
+        n = int(input())
+        values = list(map(int, input().strip().split()))
+        for i in reversed(values):
+            llist.push(i)
+        k = int(input())
+        new_head = rotateList(llist.head, k)
+        llist.head = new_head
+        llist.printList()
+        t -= 1
+
+''' This is a function problem.You only need to complete the function given below '''
+# Your task is to complete this function
+'''
+class Node:
+    def __init__(self, data):
+        self.data = data
+        self.next = None
+'''
+# This function should rotate list counter-
+# clockwise by k and return new head (if changed) 
+def rotateList(head, k):
+    # code here
+    if not head:
+        return None
+    l = length(head)
+    k = k%l
+    if not k:
+        return head
+    cur = head
+    for _ in range(k-1):
+        cur = cur.next
+    newHead = cur.next
+    newCur = cur.next
+    cur.next = None
+    while newCur.next:
+        newCur = newCur.next
+    newCur.next = head
+    return newHead
+    
+def length(head):
+    l = 0
+    while head:
+        l += 1
+        head = head.next
+    return l