For a given string formed from letters a,b,and c, find all subsequences of the form a..b...c.. where the a, b, and c can be repeated any number of times homogenously.

subsequences are considered different if the indexes of the subsequences are different

For example:

Input  : abbc

Output : 3

Subsequences are abc, abc and abbc

Input  : abcabc

Output : 7

Subsequences are abc, abc, abbc, aabc

abcc, abc and abc

int GetCountABC(string s)

{

int a = 0;

int ab = 0;

int abc = 0;

for (int i = 0; i <=s.length; i++)

{

if (s[i] = 'a')

    a = 1 + 2*a;

else if (s[i] == 'b')

    ab = a + 2*ab;

else

   abc = ab + 2*abc;

}

return abc;

}

// Alternatively, we could even try to enumerate them based on their occurrence after we separate out the mandatory abc or as many abc as we can form
// untested but only to illustrate the pattern

Int GetCountABC(List<int>Str, int start, int end)

{

If (start>=end-2) return 0;

Var A = Str.Select(x => x == 'a');

Var B = Str.Select(x => x == 'b');

Var C = Str.Select(x => x == 'c');

int count = 1; // for abc
int n  = A.Count + B.Count + C.Count - 3

For (int k = 1; k <=n; k++)

       count += GetNChooseKDP(n, k);
return count;

}