From 9b73884def8ea77e563764591a3eeb0fee1d7024 Mon Sep 17 00:00:00 2001 From: Susmith98 <33018940+susmith98@users.noreply.github.com> Date: Sun, 20 Sep 2020 01:19:37 +0530 Subject: [PATCH] Added a function that checks if given string can be rearranged to form a palindrome. (#2450) * Added check_if_string_can_be_rearranged_as_palindrome function. * Added counter implementation and benchmark function. * flake changes * Update and rename check_if_string_can_be_converted_to_palindrome.py to can_string_be_rearranged_as_palindrome.py * Update can_string_be_rearranged_as_palindrome.py * # Co-authored-by: svedire Co-authored-by: Christian Clauss --- .../can_string_be_rearranged_as_palindrome.py | 113 ++++++++++++++++++ 1 file changed, 113 insertions(+) create mode 100644 strings/can_string_be_rearranged_as_palindrome.py diff --git a/strings/can_string_be_rearranged_as_palindrome.py b/strings/can_string_be_rearranged_as_palindrome.py new file mode 100644 index 000000000..92bc3b95b --- /dev/null +++ b/strings/can_string_be_rearranged_as_palindrome.py @@ -0,0 +1,113 @@ +# Created by susmith98 + +from collections import Counter +from timeit import timeit + +# Problem Description: +# Check if characters of the given string can be rearranged to form a palindrome. +# Counter is faster for long strings and non-Counter is faster for short strings. + + +def can_string_be_rearranged_as_palindrome_counter(input_str: str = "",) -> bool: + """ + A Palindrome is a String that reads the same forward as it does backwards. + Examples of Palindromes mom, dad, malayalam + >>> can_string_be_rearranged_as_palindrome_counter("Momo") + True + >>> can_string_be_rearranged_as_palindrome_counter("Mother") + False + >>> can_string_be_rearranged_as_palindrome_counter("Father") + False + >>> can_string_be_rearranged_as_palindrome_counter("A man a plan a canal Panama") + True + """ + return sum(c % 2 for c in Counter(input_str.replace(" ", "").lower()).values()) < 2 + + +def can_string_be_rearranged_as_palindrome(input_str: str = "") -> bool: + """ + A Palindrome is a String that reads the same forward as it does backwards. + Examples of Palindromes mom, dad, malayalam + >>> can_string_be_rearranged_as_palindrome("Momo") + True + >>> can_string_be_rearranged_as_palindrome("Mother") + False + >>> can_string_be_rearranged_as_palindrome("Father") + False + >>> can_string_be_rearranged_as_palindrome_counter("A man a plan a canal Panama") + True + """ + if len(input_str) == 0: + return True + lower_case_input_str = input_str.replace(" ", "").lower() + # character_freq_dict: Stores the frequency of every character in the input string + character_freq_dict = {} + + for character in lower_case_input_str: + character_freq_dict[character] = character_freq_dict.get(character, 0) + 1 + """ + Above line of code is equivalent to: + 1) Getting the frequency of current character till previous index + >>> character_freq = character_freq_dict.get(character, 0) + 2) Incrementing the frequency of current character by 1 + >>> character_freq = character_freq + 1 + 3) Updating the frequency of current character + >>> character_freq_dict[character] = character_freq + """ + """ + OBSERVATIONS: + Even length palindrome + -> Every character appears even no.of times. + Odd length palindrome + -> Every character appears even no.of times except for one character. + LOGIC: + Step 1: We'll count number of characters that appear odd number of times i.e oddChar + Step 2:If we find more than 1 character that appears odd number of times, + It is not possible to rearrange as a palindrome + """ + oddChar = 0 + + for character_count in character_freq_dict.values(): + if character_count % 2: + oddChar += 1 + if oddChar > 1: + return False + return True + + +def benchmark(input_str: str = "") -> None: + """ + Benchmark code for comparing above 2 functions + """ + print("\nFor string = ", input_str, ":") + print( + "> can_string_be_rearranged_as_palindrome_counter()", + "\tans =", + can_string_be_rearranged_as_palindrome_counter(input_str), + "\ttime =", + timeit( + "z.can_string_be_rearranged_as_palindrome_counter(z.check_str)", + setup="import __main__ as z", + ), + "seconds", + ) + print( + "> can_string_be_rearranged_as_palindrome()", + "\tans =", + can_string_be_rearranged_as_palindrome(input_str), + "\ttime =", + timeit( + "z.can_string_be_rearranged_as_palindrome(z.check_str)", + setup="import __main__ as z", + ), + "seconds", + ) + + +if __name__ == "__main__": + check_str = input( + "Enter string to determine if it can be rearranged as a palindrome or not: " + ).strip() + benchmark(check_str) + status = can_string_be_rearranged_as_palindrome_counter(check_str) + print(f"{check_str} can {'' if status else 'not '}be rearranged as a palindrome")