Try to solve problems in JavaScript, Python, and Java.
This is TIL(memo of key learnings) for solving problems in these languages,
but mostly python.

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Solved Problems 📝

241217

• 242. Valid Anagram - my solution

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Key Learnings 🤔

what is an Anagram?

an anagram is a word or phrase formed by rearranging the characters of another word or phrase.

"listen" is an anagram of "silent."

• use all character exactly Once: every original character must appear exactly once in the rearranged word.
• strings(trimmed) have the same length: after removing spaces and punctuation, the lengths of the two strings must match.

approaches to solve anagram problems with Python.

with Counter in python: https://docs.python.org/3/library/collections.html#collections.Counter

Approach A. Check Character Frequencies
Approach B. Compare Frequency Counters

approach A: Check Character Frequencies

• length check: If the lengths of the strings are not the same, return False immediately.
• create a frequency object: use collections.Counter module for create a frequency counter for the original string.
  
• compare with target string: iterate over the target string and check if each character’s frequency matches the original.

why String is iterable in python?

Strings are iterable in Python because they are sequences of characters.
any object is considered iterable if it:

• implements the __iter__ method
• implements the __getitem__ method for accessing elements by index.

approach B: Compare Frequency Counters

use Counter to count the character frequencies for both the original and target strings.

• compare the two Counter objects directly using the == operator.

why does counter(originString) == Counter(targetString) work?

The == operator checks for equality of content, not memory location.

Two Counter objects are considered equal if they contain the exact same counts for all elements, regardless of order.

types of iterables in python

• sequence types: Strings, Lists, Tuples, Ranges (support indexing)
• set types: Sets, Frozen Sets (unordered collections)
• dictionaries: iterate over keys by default, .keys(), .values(), .items().
• generator objects: created by generator functions (using yield), generator expressions.
• file objects
• custom Iterables: objects that implement __iter__ or __getitem__ method.
• iterators

how to accessing characters in a string in java

unlike python & js, java does not support indexing with square brackets [index] for strings.

👉 java doesn’t allow operator overloading. instead, use the charAt() method

String example = "listen";
char firstChar = example.charAt(0); // l

java's HashMap vs js's Map

Functionality	Java HashMap	JavaScript Map
Get	.get(key) .getOrDefault(key, defaultValue)	.get(key)
Insert/Update	.put(key, value)	.set(key, value)
Check for Keys	.containsKey(key)	.has(key)
Clear	.clear()	.clear()
Size	.size() (method)	.size (access property)
Iterate	for (Map.Entry<Key, Value> entry : map.entrySet())	for (let [key, value] of map)

• javaScript Map allows method chaining, simplifies multiple operations:

  map.set('key1', 'value1').set('key2', 'value2');

• javaScript Map can be initialized directly during declaration. but java HashMap requires using .put() after object creation.

  // js
  const map = new Map([['key1', 'value1'], ['key2', 'value2']]);

  // java
  HashMap<String, String> map = new HashMap<>();
   map.put("key1", "value1");
   map.put("key2", "value2");

• javaScript Map preserves the insertion order of keys, whereas Java HashMap does not. (use LinkedHashMap in java for ordered HashMap)

using HashMap with Generics in java

specify the key and value types when declaring a HashMap to avoid type errors:

HashMap<Character, Integer> frequency = new HashMap<>();