Write a regular expression that can match a string that starts with at least 2, but no more than 4 digits, contains substrings aa or bb followed by at least one digit. However, the string cannot end with such a substring! The match should be case insensitive. For example, the following strings are valid: 10GhaA345c, 224Zui2bb7@ String aa3c or 1aa345c is incorrect, because it doesn't start with at least two digits. Strings 12Ghaa345 is incorrect because it ends with a matching substring aa345. String 13454Ghbb3a is incorrect because it starts with more than 4 digits. String 13Ghab3a is incorrect because it doesn't have substring aa or bb. String 12Ghaac is incorrect because it doesn't have at least one digit after aa. Requirements: Your solution must be as simple and as short as possible. Important!: String 11aa345aa3 is correct even though it has two substrings: aa345 and aa3. If you focus on the first substring aa345 then all the requirements are met. If you consider the second substring aa3 then the requirement not to have such substring at the end of the string will not be satisfied. However, since you need to find at least one matching substring, this ambiguous string will be correct. Hints: To allow case-insensitive matches please make sure you use the correct REGEX flags at the end of the regular expression. Do NOT use unnecessary flags. Do NOT use lookahead/lookbehind patterns! Your solution won't be optimal. Use shortcut \d for digits [0-9].