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

Python Server Side Programming Programming

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

Arnab Chakraborty

Updated on: 2020-08-20T07:44:51+05:30

456 Views

Kickstart Your Career

Get certified by completing the course

Get Started