Skip to content
Related Articles

Related Articles

Table of Contents

Improve Article
Save Article
Like Article

Length of longest subsequence whose difference between maximum and minimum ASCII value of characters is exactly one

  • Last Updated : 08 Jun, 2021

Given a string S consisting of lowercase English alphabets, the task is to find the length of the longest subsequence from the given string such that the difference between the largest and smallest ASCII value is exactly 1.

Examples:

Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the DSA Self Paced Course at a student-friendly price and become industry ready.  To complete your preparation from learning a language to DS Algo and many more,  please refer Complete Interview Preparation Course.

In case you wish to attend live classes with experts, please refer DSA Live Classes for Working Professionals and Competitive Programming Live for Students.

Input: S = “acbbebcg”
Output: 5
Explanation: The longest subsequence of required type is “cbbbc”, whose length is 5.
The difference between largest (‘c’) and smallest (‘b’) ASCII values is c – b = 99 – 98 = 1, which is minimum possible.



Input: S = “abcd”
Output: 2
Explanation: The longest subsequence of the required type is “ab”, whose length is 2. Other possible subsequences are “bc” and “cd”.
The difference between largest(‘b’) and smallest(‘a’) ASCII values is b – a = 98 – 97 = 1.

Naive Approach: The simplest approach to solve the problem is to generate all possible subsequences of the given string S and print the length of the subsequence which is of maximum length and having a difference between ASCII values of the largest and smallest character is exactly equal to 1. 

Time Complexity: O(N * 2N)
Auxiliary Space: O(N)

Efficient Approach: To optimize the above approach, the main idea is to use a Map to optimize the above approach. Follow the steps below to solve the problem:

  • Initialize a variable, say maxLength, that stores the maximum length of the resultant subsequence.
  • Store the frequency of characters in a Map, say M.
  • Traverse the string and for each character, say ch, check if there exists character c with ASCII value (ch – 1) in the map M or not. If found to be true, then update maxLength as the maximum of maxLength and (M[ch] + M[ch – 1]).
  • After completing the above steps, print the value of maxLength as the result.

Below is the implementation of the above approach:

C++




// C++ program for the above approach
#include <bits/stdc++.h>
using namespace std;
 
// Function to find the maximum length of
// subsequence having difference of ASCII
// value of longest and smallest character as 1
int maximumLengthSubsequence(string str)
{
    // Stores frequency of characters
    unordered_map<char, int> mp;
 
    // Iterate over characters
    // of the string
    for (char ch : str) {
        mp[ch]++;
    }
    // Stores the resultant
    // length of subsequence
    int ans = 0;
 
    for (char ch : str) {
        // Check if there exists any
        // elements with ASCII value
        // one less than character ch
        if (mp.count(ch - 1)) {
            // Size of current subsequence
 
            int curr_max = mp[ch] + mp[ch - 1];
            // Update the value of ans
            ans = max(ans, curr_max);
        }
    }
 
    // Print the resultant count
    cout << ans;
}
 
// Driver Code
int main()
{
    string S = "acbbebcg";
    maximumLengthSubsequence(S);
 
    return 0;
}
Java



// Java program for the above approach
import java.util.*;
 
class GFG{
 
// Function to find the maximum length of
// subsequence having difference of ASCII
// value of longest and smallest character as 1
static void maximumLengthSubsequence(String str)
{
     
    // Stores frequency of characters
    HashMap<Character, Integer> mp = new HashMap<>();
    for(char ch : str.toCharArray())
    {
        mp.put(ch, mp.getOrDefault(ch, 0) + 1);
    }
     
    // Stores the resultant
    // length of subsequence
    int ans = 0;
 
    for(char ch : str.toCharArray())
    {
         
        // Check if there exists any
        // elements with ASCII value
        // one less than character ch
        if (mp.containsKey((char)(ch - 1)))
        {
             
            // Size of current subsequence
            int curr_max = mp.get(ch) +
                    mp.get((char)(ch - 1));
 
            // Update the value of ans
            ans = Math.max(ans, curr_max);
        }
    }
 
    // Print the resultant count
    System.out.println(ans);
}
 
// Driver Code
public static void main(String[] args)
{
    String S = "acbbebcg";
     
    maximumLengthSubsequence(S);
}
}
 
// This code is contributed by aadityapburujwale
Python3



# Python3 program for the above approach
 
# Function to find the maximum length of
# subsequence having difference of ASCII
# value of longest and smallest character as 1
def maximumLengthSubsequence(str):
     
    # Stores frequency of characters
    mp = {}
 
    # Iterate over characters
    # of the string
    for ch in str:
        if ch in mp.keys():
            mp[ch] += 1
        else:
            mp[ch] = 1
             
    # Stores the resultant
    # length of subsequence
    ans = 0
     
    for ch in str:
         
        # Check if there exists any
        # elements with ASCII value
        # one less than character ch
        if chr(ord(ch) - 1) in mp.keys():
             
            # Size of current subsequence
            curr_max = mp[ch]
             
            if chr(ord(ch) - 1) in mp.keys():
                 curr_max += mp[chr(ord(ch) - 1)]
                  
            # Update the value of ans
            ans = max(ans, curr_max)
 
    # Print the resultant count
    print(ans)
 
# Driver Code
S = "acbbebcg"
 
maximumLengthSubsequence(S)
 
# This code is contributed by Stream_Cipher
C#



// C# program for the above approach
using System;
using System.Collections.Generic;
 
public class GFG
{
 
// Function to find the maximum length of
// subsequence having difference of ASCII
// value of longest and smallest character as 1
static void maximumLengthSubsequence(String str)
{
     
    // Stores frequency of characters
    Dictionary<char, int> mp = new Dictionary<char, int>();
    foreach(char ch in str.ToCharArray())
    {
        if(mp.ContainsKey(ch))
            mp[ch] = mp[ch] + 1;
        else
            mp.Add(ch, 1);
    }
     
    // Stores the resultant
    // length of subsequence
    int ans = 0;
    foreach(char ch in str.ToCharArray())
    {
         
        // Check if there exists any
        // elements with ASCII value
        // one less than character ch
        if (mp.ContainsKey((char)(ch - 1)))
        {
             
            // Size of current subsequence
            int curr_max = mp[ch] +
                    mp[(char)(ch - 1)];
 
            // Update the value of ans
            ans = Math.Max(ans, curr_max);
        }
    }
 
    // Print the resultant count
    Console.WriteLine(ans);
}
 
// Driver Code
public static void Main(String[] args)
{
    String S = "acbbebcg";  
    maximumLengthSubsequence(S);
}
}
 
// This code is contributed by Amit Katiyar
Javascript



<script>
      // JavaScript program for the above approach
      // Function to find the maximum length of
      // subsequence having difference of ASCII
      // value of longest and smallest character as 1
      function maximumLengthSubsequence(str) {
        // Stores frequency of characters
        var mp = {};
 
        var temp = str.split("");
        for (const ch of temp) {
          if (mp.hasOwnProperty(ch)) mp[ch] = mp[ch] + 1;
          else mp[ch] = 1;
        }
 
        // Stores the resultant
        // length of subsequence
        var ans = 0;
        for (const ch of temp) {
          // Check if there exists any
          // elements with ASCII value
          // one less than character ch
          if (mp.hasOwnProperty(String.fromCharCode(ch.charCodeAt(0) - 1))) {
            // Size of current subsequence
            var curr_max =
              mp[ch] + mp[String.fromCharCode(ch.charCodeAt(0) - 1)];
 
            // Update the value of ans
            ans = Math.max(ans, curr_max);
          }
        }
 
        // Print the resultant count
        document.write(ans);
      }
 
      // Driver Code
      var S = "acbbebcg";
      maximumLengthSubsequence(S);
       
      // This code is contributed by rdtank.
    </script>
Output: 
5
 
Time Complexity: O(N)
Auxiliary Space: O(1) 
 



My Personal Notes
arrow_drop_up
Previous
Reduce sum of any subset of an array to 1 by multiplying all its elements by any value
Next

Count occurrences of an element in a matrix of size N * N generated such that each element is equal to product of its indices
Recommended Articles
Page :
Find number of substrings of length k whose sum of ASCII value of characters is divisible by k
03, Dec 18
Sub-strings having exactly k characters that have ASCII value greater than p
03, Nov 18
Count pairs of characters in a string whose ASCII value difference is K
30, May 19
Convert all lowercase characters to uppercase whose ASCII value is co-prime with k
12, Nov 18
Subsequences generated by including characters or ASCII value of characters of given string
02, Dec 20
Minimize swaps of same-indexed characters to make sum of ASCII value of characters of both the strings odd
10, Feb 21
Length of longest non-decreasing subsequence such that difference between adjacent elements is at most one
20, Feb 21
Length of longest subsequence whose XOR value is odd
15, Jul 20
Make all characters of a string same by minimum number of increments or decrements of ASCII values of characters
10, Feb 21
Length of longest Palindromic Subsequence of even length with no two adjacent characters same
04, Feb 20
Count different Bitwise OR values of equal length strings S1 and S2 by swapping exactly one pair of characters from the first string
27, Jun 21
Count characters in a string whose ASCII values are prime
14, Dec 18
Longest subsequence having difference between the maximum and minimum element equal to K
08, Feb 21
Python program to print words from a sentence with highest and lowest ASCII value of characters
15, Mar 21
Longest Common Subsequence (LCS) by repeatedly swapping characters of a string with characters of another string
22, Mar 21
Replace every character of string by character whose ASCII value is K times more than it
01, Aug 18
Minimum length of the sub-string whose characters can be used to form a palindrome of length K
17, Apr 19
Longest subsequence such that difference between adjacents is one | Set 2
30, Oct 17
Find length of longest subsequence of one string which is substring of another string
09, Jul 17
Convert Hexadecimal value String to ASCII value String
22, May 18
Minimum length substring with exactly K distinct characters
05, Mar 19
Count of maximum occurring subsequence using only those characters whose indices are in GP
23, Aug 20
Generate a string of size N whose each substring of size M has exactly K distinct characters
21, Apr 20
Longest string in non-decreasing order of ASCII code and in arithmetic progression
09, Jul 18
Article Contributed By :
https://media.geeksforgeeks.org/auth/avatar.png
shekabhi1208
@shekabhi1208
Vote for difficulty





Improved By :
Article Tags :
Practice Tags :
Report Issue

We use cookies to ensure you have the best browsing experience on our website. By using our site, you
acknowledge that you have read and understood our
Cookie Policy &
        Privacy Policy

Lightbox

Start Your Coding Journey Now!