Count A+b+c+ Subsequences

1. You are given a string str.

2. You are required to calculate and print the count of subsequences of the nature a+b+c+.

For abbc: there are 3 subsequences. abc, abc, abbc

For abcabc: there are 7 subsequences. abc, abc, abbc, aabc, abcc, abc, abc.

Input Format

A string str

Output Format

count of subsequences of the nature a+b+c+

Constraints

0 < str.length <= 10

Sample Input

abcabc

Sample Output

7

Solution:

import java.io.*;

import java.util.*;

public class Main {

    public static void main(String[] args) throws Exception {

        // in

        Scanner sc = new Scanner(System.in);

        String str = sc.nextLine();

        sc.close();

        // process

        int a = 0, ab = 0, abc = 0, n = str.length();

        for(int i=0;i<n;i++){

            char ch = str.charAt(i);

            if(ch == 'a')

                a = 2*a + 1;

            else if(ch == 'b')

                ab = 2*ab+a;

            else if(ch == 'c')

                abc = 2*abc+ab;

        }

        System.out.println(abc);

    }

}