Unique Words Counter

This contest problem requires you to write a program to count the number of unique words in a given string.

Words are defined as contiguous sequences of alphanumeric characters (i.e. letters and digits). The comparison is case-insensitive, meaning that Hello, hello, and HELLO are considered the same word.

You can think of a word as any substring that matches the regular expression \(\b\w+\b\). Your task is to output the count of unique words found in the input.

inputFormat

The input is provided via standard input (stdin) as a single string which may contain spaces, punctuation, and newline characters.

outputFormat

Output the number of unique words as an integer to standard output (stdout).

Hello world

2