Valid Anagram

To determine if two strings are anagrams, you need to check whether they have the same characters with the same frequencies. Here’s a step-by-step guide:

  1. Check Length: If the lengths of s and t are different, return false. Anagrams must have the same length.
  2. Count Characters: Create a frequency counter for each string that counts the occurrence of each character.
  3. Compare Frequencies: Compare the frequency counters for the two strings. If they are the same, the strings are anagrams. If not, they are not anagrams.

The Python code below implements this approach:

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class Solution:
    def isAnagram(self, s: str, t: str) -> bool:
        if len(s) != len(t):
            return False

        counter_s = [0] * 26
        counter_t = [0] * 26

        for char in s:
            counter_s[ord(char) - ord('a')] += 1

        for char in t:
            counter_t[ord(char) - ord('a')] += 1

        return counter_s == counter_t

The code uses two arrays to count the occurrences of each character in the strings s and t, and then compares these arrays to determine if the strings are anagrams.

The solution runs in O(n) time complexity, where n is the length of the input strings, and O(1) space complexity, as the size of the counter arrays is constant.

Identifying Problem Isomorphism

“Valid Anagram” shares a similar concept with “Ransom Note”.

In “Valid Anagram”, you are given two strings and are required to determine whether one string is an anagram of the other, which involves checking whether they contain exactly the same characters in the same frequencies.

In “Ransom Note”, you are given two strings, one representing a ransom note and the other representing available letters. The task is to check if you can construct the ransom note from the available letters, which also boils down to checking whether one string contains all the characters (with the same frequencies) of the other string.

The two problems share the same principle: checking if characters in one string can completely cover the characters in the other string. However, they apply this principle in different contexts: checking for anagrams in one case and constructing a note in the other.

“Valid Anagram” is simpler as it just requires comparing the frequencies of characters in both strings. “Ransom Note” adds a bit of complexity as it requires checking if one string can be constructed from the other, but the core concept remains the same.

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class Solution(object):
    def isAnagram(self, s, t):
        if len(s) != len(t):
            return False
        for idx in set(s):
            if s.count(idx) != t.count(idx):
                return False
        return True

Problem Classification

This problem can be classified as follows:

  • Problem Domain: String Manipulation, Anagram detection.
  • Techniques Used: Sorting, Frequency Counting, Comparison
  • Concepts Involved: String comparison, Character Frequency Counting
  • Data Structures: Strings

The problem falls under the category of string manipulation where the main goal is to determine if one string is an anagram of another. This involves understanding the concept of anagrams, which is a critical part of the problem domain. The techniques used include sorting and comparison which are typical in problems that involve checking the equivalency of strings. This problem also involves counting the frequency of characters in both strings which is a common technique used in string manipulation problems. The problem uses strings as the main data structure.

Language Agnostic Coding Drills

  1. Understanding problem statement and function signature: In this case, the problem statement asks to determine if two input strings are anagrams of each other. The function takes two input strings and returns a boolean value.

  2. Understanding basic Python syntax: Understanding how to create a class and methods in Python, the syntax of conditional statements (if-else), and looping constructs (for loop).

  3. Working with strings and their properties: Understanding how strings work in Python, including how to determine the length of a string (len()), how to iterate over a string, and how to count occurrences of a particular character in a string using count().

  4. Working with sets: The set data type is used in this problem to get unique characters from the string. It’s important to understand how sets work, how to create them, and how to use them in loops.

  5. Logical reasoning and algorithm creation: Finally, the actual logic of the problem involves comparing the lengths of the strings and then comparing the count of each unique character in the two strings. If the counts are not the same for any character, the function returns False, indicating that the strings are not anagrams. If no such characters are found, it returns True.

As for the approach, it can be described as follows:

  1. Check if the lengths of the two strings are equal. If they’re not, they cannot be anagrams, so return False.

  2. Create a set of unique characters from one of the strings.

  3. Loop through the unique characters, and for each character, count how many times it appears in both strings. If the counts are not equal for any character, return False.

  4. If the function has not returned False by this point, that means the counts matched for all characters and the strings are anagrams, so return True.

Targeted Drills in Python

  1. Understanding problem statement and function signature:

    This isn’t a coding drill per se, but it’s crucial to understand what the problem asks for. For instance, write a simple function that takes two inputs and returns a boolean value.

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    def are_numbers_equal(num1, num2):
    return num1 == num2

  2. Understanding basic Python syntax:

    Understanding Python syntax can be practiced by writing a simple conditional statement and loop.

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    def is_even(num):
    if num % 2 == 0:
        return True
    else:
        return False

    Here, we learn about the ‘if-else’ construct and modulus operator (%).

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    def print_numbers(num):
    for i in range(num):
        print(i)

    Here, we learn about ‘for’ loops and the ‘range()’ function.

  3. Working with strings and their properties:

    Let’s practice counting the occurrences of a character in a string:

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    def count_character_in_string(s, char):
    return s.count(char)

  4. Working with sets:

    Practice creating a set from a string and looping through it:

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    def print_unique_chars(s):
    unique_chars = set(s)
    for char in unique_chars:
        print(char)

  5. Logical reasoning and algorithm creation:

    For the final solution, we combine all these drills:

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    class Solution(object):
    def isAnagram(self, s, t):
        if len(s) != len(t):
            return False
        for idx in set(s):
            if s.count(idx) != t.count(idx):
                return False
        return True

    This function first checks the lengths of the two input strings. If the lengths are unequal, it immediately returns False. If the lengths are equal, it proceeds to compare the frequency of each unique character in both strings. If it finds a character whose frequency is different in the two strings, it returns False. If no such characters are found, it returns True, indicating the strings are anagrams.