Find the lexicographically largest palindromic Subsequence of a String in Python

Suppose we have a string S; we have to find the lexicographically largest palindromic subsequence of that string.

So, if the input is like "tutorialspointtutorial", then the output will be "uu"

To solve this, we will follow these steps −

• ans := blank string

• max_val := s[0]

• for i in range 1 to size of s, do

  • max_val := maximum of max_val, s[i]

• for i in range 0 to size of s, do

  • if s[i] is same as max_val, then

    • ans := ans + s[i]

• return ans

Example 

Let us see the following implementation to get better understanding −

def largest_palindromic_substr(s):
   ans = ""
   max_val = s[0]
   for i in range(1, len(s)):
      max_val = max(max_val, s[i])
   for i in range(0, len(s)):
      if s[i] == max_val:
         ans += s[i]
   return ans

s = "tutorialspointtutorial"
print(largest_palindromic_substr(s))

Input

"tutorialspointtutorial"

Output

uu