Lesson 02 · Adding words, case-insensitively

Adding words, case-insensitively

A dictionary you cannot fill is useless. Today you add words to it and make membership ignore case, so "Apple", "apple", and "APPLE" are all the same known word.

The goal

Store added words and make Contains match regardless of the case of either the stored word or the query.

Start here - the target

TO DO

Scenario: Adding a word and matching it in any case

Givenan empty dictionary

WhenAdd("Apple") is called

ThenContains("apple") is true, Contains("APPLE") is true, and Contains("Apple") is true

AndContains("banana") is still false

Background

Spelling is not about capitalization - Apple at the start of a sentence and apple mid-sentence are the same word, and a checker that flagged one because it learned the other would be useless. The fix is normalization: fold every word to a single canonical form (lower case) both when you store it and when you look it up. Do it in one small helper so the two paths can never drift apart.

A set is the natural home for the words - you only care whether a word is present, not how many times or in what order (that changes later, when frequency starts to matter). Storing the normalized form means the set holds apple, and any casing of the query normalizes to the same key and hits.

Make it work

// fold case ONCE, on the way in and on the way out, so the
// stored form and the query form always agree
func normalize(word string) string { /* lower-case it */ }
func (d *Dictionary) Add(word string) {
  // store normalize(word) in a set
}
func (d *Dictionary) Contains(word string) bool {
  // look up normalize(word)
}

CheckpointDONE

The dictionary holds words and matches them case-insensitively. Commit and stop here.