Python program to count the pairs of reverse strings

Last Updated : 11 Dec, 2020

Given the String list, write a Python program to count pairs of reverse strings.

Examples:

Input : test_list = [“geeks”, “best”, “tseb”, “for”, “skeeg”]
Output : 2
Explanation : geeks, skeeg and best, tseb are 2 pairs of reverse strings available.
Input : test_list = [“geeks”, “best”, “for”, “skeeg”]
Output : 1
Explanation : geeks, skeeg is 1 pair of reverse strings available.

Method #1 : Using reversed() + loop

In this, we perform task of comparing strings to reversed version of it using reversed() and conditional statements. In this, loop is used for task of comparing with each string for pairing.

Python3

# Python3 code to demonstrate working of
# Reversed Pairs in Strings List
# Using reversed() + loop
  
# initializing Matrix
test_list = ["geeks", "best", "tseb", "for", "skeeg"]
  
# printing original list
print("The original list is : " + str(test_list))
  
res = 0
for idx in range(0, len(test_list)):
  
    # nested loop to check with each element with possible reverse counterpart
    for idxn in range(idx, len(test_list)):
        if test_list[idxn] == str(''.join(list(reversed(test_list[idx])))):
            res += 1
  
# printing result
print("Reversed Pairs : " + str(res))

Output:

The original list is : [‘geeks’, ‘best’, ‘tseb’, ‘for’, ‘skeeg’]
Reversed Pairs : 2

Method #2 : Using list comprehension + sum()

In this, list comprehension handles nested loop and sum() handles part of increment counter for counting pairs.

Python3

# Python3 code to demonstrate working of
# Reversed Pairs in Strings List
# Using list comprehension + sum()
  
# initializing Matrix
test_list = ["geeks", "best", "tseb", "for", "skeeg"]
  
# printing original list
print("The original list is : " + str(test_list))
  
# list comprehension for nested loop
# sum increments counts
res = sum([1 for idx in range(0, len(test_list)) for idxn in range(idx, len(
    test_list)) if test_list[idxn] == str(''.join(list(reversed(test_list[idx]))))])
  
# printing result
print("Reversed Pairs : " + str(res))