Program to find number of subsequences with i, j and k number of x, y, z letters in Python

Suppose we have a string s with "x", "y" and "z"s, we have to find the number of subsequences that have i number of "x" characters, followed by j number of "y" characters and followed by k number of "z" characters where i, j, k ≥ 1.

So, if the input is like s = "xxyz", then the output will be 3, as we can make two "xyz" and one "xxyz"

To solve this, we will follow these steps:

• n := size of s

• x := 0, y := 0, z := 0

• for i in range 0 to n, do

  • count := 0

  • if s[i] is same as "x", then

    • x := x * 2

    • x := x + 1

  • if s[i] is same as "y", then

    • y := y * 2

    • y := y + x

  • if s[i] is same as "z", then

    • z := z * 2

    • z := z + y

• return z

Example

 Live Demo

class Solution:
   def solve(self, s):
      n = len(s)

      x = 0
      y = 0
      z = 0
      for i in range(n):
         count = 0
         if s[i] == "x":
            x *= 2
            x += 1
         if s[i] == "y":
            y *= 2
            y += x
         if s[i] == "z":
            z *= 2
            z += y

      return z

ob = Solution()
print(ob.solve("xxyz"))

Input

"xxyz"

Output

3