How should I practice Count Repeated Words?

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Problem · String

Count Repeated Words

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● Easy

DatadogINTERNPHONE SCREEN

Problem statement

Given a paragraph, count how many distinct words occur at least twice. Matching is case-insensitive, so differently capitalized forms of the same word belong to one group.

The only punctuation marks in the paragraph are periods and commas, and they are used correctly. Punctuation is not part of a word. A word that appears two or more times contributes exactly 1 to the answer, regardless of how many total occurrences it has.

Function

countRepeatedWords(paragraph: String) → int

Examples

Example 1

paragraph = "Sun rises, and sun sets."return = 1

Sun and sun are the same word after case normalization, so sun contributes one.

Example 2

paragraph = "Go, go. GO, stay."return = 1

go appears three times but still contributes only one distinct repeated word.

Example 3

paragraph = "Hello, world."return = 0

Neither word repeats.

Constraints

1 <= paragraph.length <= 200000
The paragraph contains English letters, spaces, periods, and commas only.
Periods and commas are used correctly and separate from the words they punctuate.
The paragraph contains at least one word.