Python – Swap K suffix with prefix
Given a List, perform a swap of K prefix and suffix.
Examples:
Input : test_list = [5, 6, 3, 1, 0, 1, 3, 5, 7, 9], K = 2
Output : [7, 9, 3, 1, 0, 1, 3, 5, 5, 6]Explanation : Rear 2 and Front 2 elements swapped.Input : test_list = [5, 6, 3, 1, 0, 1, 3, 5, 7, 9], K = 1
Output : [9, 6, 3, 1, 0, 1, 3, 5, 7, 5]Explanation : Rear 1 and Front 1 element swapped.
Method #1: Using slice and range swap
In this, we perform the task of getting the required slice using list slicing and perform range swap to swap elements. This is inplace method to solve this problem.
Python3
# Python3 code to demonstrate working of# Swap K suffix with prefix# Using range swap + slice()# initializing listtest_list = [5, 6, 3, 1, 0, 1, 3, 5, 7, 9]# printing original listprint("The original list is : " + str(test_list))# initializing KK = 3# performing range swaptest_list[:K], test_list[len( test_list) - K:] = test_list[len(test_list) - K:], test_list[:K]# printing resultprint("After prefix suffix swap : " + str(test_list)) |
The original list is : [5, 6, 3, 1, 0, 1, 3, 5, 7, 9] After prefix suffix swap : [5, 7, 9, 1, 0, 1, 3, 5, 6, 3]
Time Complexity: O(1)
Auxiliary Space: O(1)
Method #2 : Using slice notation
In this we perform reconstruction of list elements using slicing each list performing slice.
Python3
# Python3 code to demonstrate working of# Swap K suffix with prefix# Using slice notation# initializing listtest_list = [5, 6, 3, 1, 0, 1, 3, 5, 7, 9]# printing original listprint("The original list is : " + str(test_list))# initializing KK = 3# joining parts using sliceres = test_list[len(test_list) - K:] + \ test_list[K: len(test_list) - K] + test_list[:K]# printing resultprint("After prefix suffix swap : " + str(res)) |
The original list is : [5, 6, 3, 1, 0, 1, 3, 5, 7, 9] After prefix suffix swap : [5, 7, 9, 1, 0, 1, 3, 5, 6, 3]
Time Complexity: O(n) where n is the number of elements in the list “test_list”. sliceperforms n number of operations.
Auxiliary Space: O(1), no extra space is required
Method 3: Using a loop to swap elements
Step-by-step approach:
- Initialize two pointers, i and j, both pointing to the beginning of the list.
- Move j K steps forward.
- Swap the elements at positions i and len(test_list)-K+i.
- Increment i and decrement j until they meet at the middle of the list.
- The K suffix and prefix have now been swapped.
Python3
# Python3 code to demonstrate working of# Swap K suffix with prefix# Using a loop to swap elements# initializing listtest_list = [5, 6, 3, 1, 0, 1, 3, 5, 7, 9]# printing original listprint("The original list is : " + str(test_list))# initializing KK = 3# swap suffix with prefix using loopi = 0j = len(test_list) - Kwhile j < len(test_list): test_list[i], test_list[j] = test_list[j], test_list[i] i += 1 j += 1# printing resultprint("After prefix suffix swap : " + str(test_list)) |
The original list is : [5, 6, 3, 1, 0, 1, 3, 5, 7, 9] After prefix suffix swap : [5, 7, 9, 1, 0, 1, 3, 5, 6, 3]
Time complexity: O(K)
Auxiliary space: O(1).
Method #4: Using List Comprehension
Step-by-step approach:
- Create two slices of the original list, one for the prefix and one for the suffix.
- Reverse the suffix slice using the slice notation.
- Use list comprehension to create a new list with the swapped suffix and prefix slices, followed by the remaining middle part of the list.
- Return the final swapped list.
Python3
# Python3 code to demonstrate working of# Swap K suffix with prefix# Using list comprehension# initializing listtest_list = [5, 6, 3, 1, 0, 1, 3, 5, 7, 9]# printing original listprint("The original list is : " + str(test_list))# initializing KK = 3# create two slices for prefix and suffixprefix = test_list[:K]suffix = test_list[-K:]# reverse the suffix slicesuffix = suffix[::-1]# use list comprehension to create new list with swapped suffix and prefix slices, and the remaining middle partswapped_list = [item for sublist in [suffix, test_list[K:-K], prefix] for item in sublist]# printing resultprint("After prefix suffix swap : " + str(swapped_list)) |
The original list is : [5, 6, 3, 1, 0, 1, 3, 5, 7, 9] After prefix suffix swap : [9, 7, 5, 1, 0, 1, 3, 5, 6, 3]
Time complexity: O(n)
Auxiliary space: O(n)
