Score : $200$ points
You are given a string $S$ of length $N$. Among its subsequences, count the ones such that all characters are different, modulo $10^9+7$. Two subsequences are considered different if their characters come from different positions in the string, even if they are the same as strings.
Here, a subsequence of a string is a concatenation of one or more characters from the string without changing the order.
Input is given from Standard Input in the following format:
Print the number of the subsequences such that all characters are different, modulo $10^9+7$.
Since all characters in $S$ itself are different, all its subsequences satisfy the condition.
The answer is five:
b, two occurrences of
a, two occurrences of
ba. Note that we do not count
baa, since it contains two