Program to find minimum number of monotonous string groups in Python

Suppose we have a lowercase string s. We have to find the minimum numbers of contiguous substrings in which s is divided into parts such that each substring is either non-increasing or non-decreasing. So for example, if the string is like "pqqqr" is a non-decreasing string, and "qqqp" is a non-increasing string.

So, if the input is like s = "pqrsrqp", then the output will be 2, because we can break s like "pqrs" and "rqp".

To solve this, we will follow these steps −

• if s is empty, then

  • return 0

• last := s[0]

• direction := 1

• count := 1

• for each char in s, do

  • if char > last, then

    • if direction is same as 1, then

      • direction := 0

    • otherwise when direction is same as 2, then

      • direction := 1

      • count := count + 1

  • otherwise when char < last, then

    • if direction is same as 1, then

      • direction := 2

    • otherwise when direction is same as 0, then

      • direction := 1

      • count := count + 1

  • last := char

• return count

Example

Let us see the following implementation to get better understanding

def solve(s):
   if not s:
      return 0

   last = s[0]
   direction = 1
   count = 1

   for char in s:
      if char > last:
         if direction == 1:
            direction = 0
         elif direction == 2:
            direction = 1
            count += 1
      elif char < last:
         if direction == 1:
            direction = 2
         elif direction == 0:
            direction = 1
            count += 1
      last = char

   return count

s = "pqrsrqp"
print(solve(s))

Input

"pqrsrqp"

Output

2