Regular Expression To Validate Months.

Solution 1 - The solution is ^(0[1-9]|1[012])$

Result - The above regular expression allows 

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Solution 2 - The solution is ^([1-9]|1[012])$

Result - The above regular expression allows 

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Solution 3 - This integrated solution 1 and solution 2 ^(0?[1-9]|1[012])$

Result - The above regular expression allows 

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Hint - ? symbol in regular expression is used to match whether the character before question mark (?) is present or absent.. both will return true..