Find the lexicographically smallest string which satisfies the given condition in Python

PythonServer Side ProgrammingProgramming

Suppose we have an array A of n numbers, where A[i] indicates the number of distinct characters in the prefix of length (i + 1) of a string s, we have to find the lexicographically smallest string that satisfies the given prefix array. All characters will be lowercase English alphabets [a-z]. If there is no such string then return -1.

So, if the input is like A = [1,1,2,3,4], then the output will be aabcd as prefix[0] has 1 distinct character, prefix[1] has 1 distinct character, prefix[2] has 2 distinct characters, prefix[3] has 3 distinct characters, prefix[4] has 4 distinct characters and the string is smallest.

To solve this, we will follow these steps −

  • n := size of A

  • character := 'a'

  • string := blank string

  • if n < 1 or A[0] is not 1, then

    • return -1

  • string := string concatenate character

  • character := next character of this current character

  • for i in range 1 to n, do

    • difference := A[i] - A[i - 1]

    • if difference > 1 or difference < 0 or A[i] > 26, then

      • return -1

    • otherwise when difference is same as 0, then

      • string := string concatenate 'a'

    • otherwise,

      • string := string concatenate character

      • character := next character of this current character

  • return string

Example 

Let us see the following implementation to get better understanding −

 Live Demo

def get_smallest_string(A):
   n = len(A)
   character = 'a'
   string = ""
   if (n < 1 or A[0] != 1):
      return -1
   string += str(character)
   character = chr(ord(character) + 1)
   for i in range(1, n):
      difference = A[i] - A[i - 1]
      if (difference > 1 or difference < 0 or A[i] > 26):
         return -1
      elif (difference == 0):
         string += 'a'
      else:
         string += character
         character = chr(ord(character) + 1)
return string

A = [1, 1, 2, 3, 4]
print(get_smallest_string(A))

Input

[1, 1, 2, 3, 4]

Output

aabcd
raja
Published on 20-Aug-2020 11:14:20
Advertisements