Memory App

Some examples

Find variable names

Variable names are allowed to contain only alphanumeric characters and underscores, but not begin with a digit. Regex [a-zA-Z_][a-zA-Z_0-9]*

Find string with double-quotes

We match all characters except a double quote, and apply quantifier. Regex "[^"]+"

Time of the day 9:17 AM or 12:30 PM

Something like [0-9]?[0-9]:[0-9][0-9] matches 9:17 or 12:30, but also allows 99:99 Looking at the hour, we realize that if it is a two-digit number, the first digit must be 1. But, 1?[0-9] still allows 19, which is wrong. We can use alternation for the hour part ([1-9]|1[012]). The correct regex is ([0-9]|1[012]):[0-5][0-9] (am|pm)

Time of the day 00:01 to 23:59

Regex is [01]?[0-9]|2[0-3]:[0-5][0-9]
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