Maximum number of characters between any two same character in a string

Given a string, find the maximum number of characters between any two same character in the string. If no character repeats, print -1.
Examples:

Input : str = "abba"
Output : 2
The maximum number of characters are
between two occurrences of 'a'.

Input : str = "baaabcddc"
Output : 3
The maximum number of characters are
between two occurrences of 'b'.

Input : str = "abc"
Output : -1

Recommended: Please solve it on “PRACTICE” first, before moving on to the solution.

Approach 1 (Simple): Use two nested loops. The outer loop picks character from left to right, the inner loop finds farthest occurrence and keeps track of maximum.

C++

// Simple C++ program to find maximum number 
// of characters between two occurrences of 
// same character 
#include <bits/stdc++.h> 
using namespace std; 
  
int maximumChars(string& str) 
{ 
    int n = str.length(); 
    int res = -1; 
    for (int i = 0; i < n - 1; i++) 
        for (int j = i + 1; j < n; j++) 
            if (str[i] == str[j]) 
                res = max(res, abs(j - i - 1)); 
    return res; 
} 
  
// Driver code 
int main() 
{ 
    string str = "abba"; 
    cout << maximumChars(str); 
    return 0; 
} 

Java

// Simple Java program to find maximum 
// number of characters between two 
// occurrences of same character 
class GFG { 
      
    static int maximumChars(String str) 
    { 
        int n = str.length(); 
        int res = -1; 
          
        for (int i = 0; i < n - 1; i++) 
            for (int j = i + 1; j < n; j++) 
                if (str.charAt(i) == str.charAt(j)) 
                    res = Math.max(res,  
                         Math.abs(j - i - 1)); 
                           
        return res; 
    } 
      
    // Driver code 
    public static void main(String[] args) 
    { 
        String str = "abba"; 
          
        System.out.println(maximumChars(str)); 
    } 
} 
  
// This code is contributed by vt_m. 

Python3

# Simple Python3 program to find maximum number 
# of characters between two occurrences of 
# same character 
def maximumChars(str): 
    n = len(str) 
    res = -1
    for i in range(0, n - 1): 
        for j in range(i + 1, n): 
            if (str[i] == str[j]): 
                res = max(res, abs(j - i - 1)) 
    return res 
  
# Driver code 
if __name__ == '__main__': 
    str = "abba"
    print(maximumChars(str)) 
  
# This code is contributed by PrinciRaj1992  

C#

// Simple C# program to find maximum 
// number of characters between two 
// occurrences of same character 
using System; 
  
public class GFG { 
      
    static int maximumChars(string str) 
    { 
        int n = str.Length; 
        int res = -1; 
          
        for (int i = 0; i < n - 1; i++) 
            for (int j = i + 1; j < n; j++) 
                if (str[i] == str[j]) 
                    res = Math.Max(res,  
                         Math.Abs(j - i - 1)); 
                           
        return res; 
    } 
      
    // Driver code 
    static public void Main () 
    { 
        string str = "abba"; 
          
        Console.WriteLine(maximumChars(str)); 
    } 
} 
  
// This code is contributed by vt_m. 

Output:

Time Complexity : O(n^2)

Approach 2 (Efficient) : Initialize an array”FIRST” of length 26 in which we have to store first occurrence of an alphabet in the string and another array “LAST” of length 26 in which we will store last occurrence of the alphabet in the string here index 0 is correspond to alphabet a, 1 for b and so on . After that we will take the difference of last and first arrays to find max difference if they are not at same position.

C++

// Efficient C++ program to find maximum number 
// of characters between two occurrences of 
// same character 
#include <bits/stdc++.h> 
using namespace std; 
  
const int MAX_CHAR = 256; 
  
int maximumChars(string& str) 
{ 
    int n = str.length(); 
    int res = -1; 
  
    // Initialize all indexes as -1. 
    int firstInd[MAX_CHAR]; 
    for (int i = 0; i < MAX_CHAR; i++) 
        firstInd[i] = -1; 
  
    for (int i = 0; i < n; i++) { 
        int first_ind = firstInd[str[i]]; 
  
        // If this is first occurrence  
        if (first_ind == -1) 
            firstInd[str[i]] = i; 
  
        // Else find distance from previous 
        // occurrence and update result (if 
        // required).  
        else
            res = max(res, abs(i - first_ind - 1)); 
    } 
    return res; 
} 
  
// Driver code 
int main() 
{ 
    string str = "abba"; 
    cout << maximumChars(str); 
    return 0; 
} 

Java

// Efficient java program to find maximum 
// number of characters between two 
// occurrences of same character 
import java.io.*; 
  
public class GFG { 
  
    static int MAX_CHAR = 256; 
      
    static int maximumChars(String str) 
    { 
        int n = str.length(); 
        int res = -1; 
      
        // Initialize all indexes as -1. 
        int []firstInd = new int[MAX_CHAR]; 
          
        for (int i = 0; i < MAX_CHAR; i++) 
            firstInd[i] = -1; 
      
        for (int i = 0; i < n; i++) 
        { 
            int first_ind = firstInd[str.charAt(i)]; 
      
            // If this is first occurrence  
            if (first_ind == -1) 
                firstInd[str.charAt(i)] = i; 
      
            // Else find distance from previous 
            // occurrence and update result (if 
            // required).  
            else
                res = Math.max(res, Math.abs(i 
                                  - first_ind - 1)); 
        } 
          
        return res; 
    } 
      
    // Driver code 
      
    static public void main (String[] args) 
    { 
        String str = "abba"; 
          
        System.out.println(maximumChars(str)); 
    } 
} 
  
// This code is contributed by vt_m. 

Python3

# Efficient Python3 program to find maximum  
# number of characters between two occurrences  
# of same character 
  
MAX_CHAR = 256
  
def maximumChars(str1): 
  
    n = len(str1) 
    res = -1
  
    # Initialize all indexes as -1. 
    firstInd = [-1 for i in range(MAX_CHAR)] 
  
    for i in range(n):  
        first_ind = firstInd[ord(str1[i])] 
  
        # If this is first occurrence  
        if (first_ind == -1): 
            firstInd[ord(str1[i])] = i 
  
        # Else find distance from previous 
        # occurrence and update result (if 
        # required).  
        else: 
            res = max(res, abs(i - first_ind - 1)) 
      
    return res 
  
# Driver code 
str1 = "abba"
print(maximumChars(str1)) 
  
# This code is contributed by Mohit kumar 29 

C#

// Efficient C# program to find maximum 
// number of characters between two 
// occurrences of same character 
using System; 
  
public class GFG { 
  
    static int MAX_CHAR = 256; 
      
    static int maximumChars(string str) 
    { 
        int n = str.Length; 
        int res = -1; 
      
        // Initialize all indexes as -1. 
        int []firstInd = new int[MAX_CHAR]; 
          
        for (int i = 0; i < MAX_CHAR; i++) 
            firstInd[i] = -1; 
      
        for (int i = 0; i < n; i++) 
        { 
            int first_ind = firstInd[str[i]]; 
      
            // If this is first occurrence  
            if (first_ind == -1) 
                firstInd[str[i]] = i; 
      
            // Else find distance from previous 
            // occurrence and update result (if 
            // required).  
            else
                res = Math.Max(res, Math.Abs(i  
                              - first_ind - 1)); 
        } 
          
        return res; 
    } 
      
    // Driver code 
  
    static public void Main () 
    { 
        string str = "abba"; 
          
        Console.WriteLine(maximumChars(str)); 
    } 
} 
  
// This code is contributed by vt_m. 

Output:

Time Complexity : O(n)

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My Personal Notes

Recommended: Please solve it on “PRACTICE” first, before moving on to the solution.

C++

Java

Python3

C#

C++

Java

Python3

C#

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