Syntax error Program to change minimum characters to satisfy one of three conditions in Python

Program to change minimum characters to satisfy one of three conditions in Python

Suppose we have two strings s and t with only lowercase letters. In one operation, we can change any character in s or t to any lowercase letter. We have to satisfy one of the following three conditions −

  • Every letter in s is strictly smaller than every letter in t in the alphabet.

  • Every letter in t is strictly smaller than every letter in s in the alphabet.

  • Both s and t consist of only one distinct letter.

We have to find the minimum number of operations required to get the result.

So, if the input is like s = "sts", t = "uss", then the output will be 2 because

  • If we change t to "uuu" in 2 operations, then every letter in s is less than every letter in t.

  • If we change s to "ttt" and t to "sss" in 3 operations, then every letter in t is less than every letter in s.

  • If we change s to "sss" and t to "sss" in 2 operations, then s and t consist of one distinct letter.

Here best way was done in 2 operations (either 1 or 3).

To solve this, we will follow these steps −

  • counter_s := map to hold frequency of each character in s
  • counter_t := map to hold frequency of each character in t
  • less_s := infinity, less_t := infinity, unique := infinity
  • accu_s := 0, accu_t := 0
  • for each character c in lowercase English character, do
    • unique := minimum of unique and (size of s + size of t - counter_s[c] - counter_t[c])
      • counter_t[c])
    • if ascii of c is greater than ascii of 'a', then
      • less_a := minimum of less_s and (size of s - accu_s + accu_t)
      • less_b := minimum of less_t and (size of t - accu_t + accu_s)
    • accu_s := accu_s + counter_s[c]
    • accu_t := accu_t + counter_t[c]
  • return minimum of less_s, less_t and unique

Example

Let us see the following implementation to get better understanding −

from collections import Counter
import string
def solve(s, t):
   counter_s = Counter(s)
   counter_t = Counter(t)
   less_s, less_t, unique = float('inf'), float('inf'), float('inf')
   accu_s, accu_t = 0, 0
   for c in string.ascii_lowercase:
      unique = min(unique, len(s) + len(t) - counter_s[c] - counter_t[c])
      if c > 'a':
         less_a = min(less_s, len(s) - accu_s + accu_t)
         less_b = min(less_t, len(t) - accu_t + accu_s)
      accu_s += counter_s[c]
      accu_t += counter_t[c]
   return min(less_s, less_t, unique)

s = "sts"
t = "uss"
print(solve(s, t))

Input

"sts", "uss"

Output

2
Updated on: 2021-10-07T11:10:15+05:30

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