Need to find an input of length 26 characters and the charset should be: [a-zA-Z0-9]{26}

An integer mapping is generated which is used to rearrange the characters in the input. Then a check is performed on the rearranged characters of the input and it should be such that the ASCII value of character in each position should be less than the ASCII value of all the characters after it in the string.

So, we have to find an input such that when the characters of the input are shuffled, we get a string which satisfies the above requirements.

http://www.pwncode.club/2018/11/gofuscated-square-ctf-2018.html