Lexicographically largest string formed from the characters in range L and R

Given a string S and a range L and R, the task is to print the lexicographically largest string that can be formed from the characters in range L and R.

Examples:

Input: str = "thgyfh", L = 2, R = 6  
Output: yhhgf

Input: str = "striver", L = 3, R = 5
Output: vri

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach:

Iterate from min(L, R) to max(L, R) and increase the frequencies of characters in a freq[] array.
Iterate from 25 to 0 and print the number of times every character occurs to get the lexicographically largest string.

The common point of mistake which everyone does is they iterate from L to R instead of min(L, R) to max(L, R).

Below is the implementation of the above approach:

C++

// C++ program to print the 
// lexicographically largest string that 
// can be formed from the characters 
// in range L and R 
  
#include <bits/stdc++.h> 
using namespace std; 
  
// Function to return the lexicographically largest string 
string printLargestString(string s, int l, int r) 
{ 
    // hash array 
    int freq[26] = { 0 }; 
  
    // make 0-based indexing 
    l--; 
    r--; 
  
    // iterate and count frequencies of character 
    for (int i = min(l, r); i <= max(l, r); i++) { 
        freq[s[i] - 'a']++; 
    } 
  
    // ans string 
    string ans = ""; 
  
    // iterate in frequency array 
    for (int i = 25; i >= 0; i--) { 
  
        // add til all characters 
        // are added 
        while (freq[i]) { 
            ans += char('a' + i); 
            freq[i]--; 
        } 
    } 
  
    return ans; 
} 
  
// Driver Code 
int main() 
{ 
    string s = "striver"; 
    int l = 3, r = 5; 
    cout << printLargestString(s, l, r); 
    return 0; 
} 

Java

// Java program to print the  
// lexicographically largest String that  
// can be formed from the characters  
// in range L and R   
  
class GFG { 
  
// Function to return the lexicographically largest String  
    static String printLargestString(String s, int l, int r) { 
        // hash array  
        int freq[] = new int[26]; 
  
        // make 0-based indexing  
        l--; 
        r--; 
  
        // iterate and count frequencies of character  
        for (int i = Math.min(l, r); i <= Math.max(l, r); i++) { 
            freq[s.charAt(i) - 'a']++; 
        } 
  
        // ans String  
        String ans = ""; 
  
        // iterate in frequency array  
        for (int i = 25; i >= 0; i--) { 
  
            // add til all characters  
            // are added  
            while (freq[i] > 0) { 
                ans += (char) ('a' + i); 
                freq[i]--; 
            } 
        } 
  
        return ans; 
    } 
  
// Driver Code  
    public static void main(String[] args) { 
  
        String s = "striver"; 
        int l = 3, r = 5; 
        System.out.println(printLargestString(s, l, r)); 
  
    } 
} 
/* This JAVA code is contributed by 29AjayKumar*/

Python 3

# Python 3 program to print the 
# lexicographically largest string that 
# can be formed from the characters 
# in range L and R 
  
# Function to return the lexicographically  
# largest string 
def printLargestString(s, l, r): 
  
    # hash array 
    freq = [0] * 26
  
    # make 0-based indexing 
    l -= 1
    r -= 1
  
    # iterate and count frequencies of character 
    for i in range(min(l, r), max(l, r) + 1) : 
        freq[ord(s[i]) - ord('a')] += 1
  
    # ans string 
    ans = "" 
  
    # iterate in frequency array 
    for i in range(25, -1, -1): 
  
        # add til all characters are added 
        while (freq[i]): 
            ans += chr(ord('a') + i) 
            freq[i] -= 1
  
    return ans 
  
# Driver Code 
if __name__ == "__main__": 
      
    s = "striver"
    l = 3
    r = 5
    print(printLargestString(s, l, r)) 
  
# This code is contributed by ita_c 

C#

// C# program to print the lexicographically 
// largest String that can be formed from the  
// characters in range L and R 
using System; 
  
class GFG 
{ 
  
// Function to return the lexicographically  
// largest String  
static String printLargestString(String s,  
                                 int l, int r)  
{ 
    // hash array  
    int []freq = new int[26]; 
  
    // make 0-based indexing  
    l--; 
    r--; 
  
    // iterate and count frequencies 
    // of character  
    for (int i = Math.Min(l, r);  
             i <= Math.Max(l, r); i++) 
    { 
        freq[s[i] - 'a']++; 
    } 
  
    // ans String  
    String ans = ""; 
  
    // iterate in frequency array  
    for (int i = 25; i >= 0; i--) 
    { 
  
        // add til all characters  
        // are added  
        while (freq[i] > 0)  
        { 
            ans += (char) ('a' + i); 
            freq[i]--; 
        } 
    } 
  
    return ans; 
} 
  
// Driver Code  
public static void Main()  
{ 
    String s = "striver"; 
    int l = 3, r = 5; 
    Console.Write(printLargestString(s, l, r)); 
} 
} 
  
// This code is contributed by 29AjayKumar 

Output:

vri

Time Complexity – O(N)
Each element gets added to the frequency table only once which takes O(1) and is appended to string which also takes O(1).

My Personal Notes

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

C++

Java

Python 3

C#

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