使用正则表达式在字符串中的任意位置多次查找字符

Question

I'm generating all possible permutations of a string 10 characters long with the numbers 1, 2, 3 .

I now want to check to see how many of the strings have the number 1 three times, 2 two times and 3 five times.

What is the correct regex for this if I am using egrep?

Answer 1

You can use positive lookaheads :

(?=(.*1){3})(?=(.*2){2})(?=(.*3){5})^.{10}$

See it in action

However, note that this is not the perfect task to solve with regexes.

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EDIT : Since you said you are using egrep , you can use piping instead:

echo 3121233133 | egrep '(.*1){3}' | egrep '(.*2){2}'| egrep '(.*3){5}' | egrep '^.{10}$'

Answer 2

This would be faster than regex:

input.replace("1", "").length === input.length - 3 &&
input.replace("2", "").length === input.length - 2 &&
input.replace("3", "").length === input.length - 5;