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

Given a string, find the maximum number of characters between any two characters 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

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

Javascript

<script>
    // Simple Javascript program to find maximum
    // number of characters between two
    // occurrences of same character

    function maximumChars(str)
    {
        let n = str.length;
        let res = -1;

        for (let i = 0; i < n - 1; i++)
            for (let j = i + 1; j < n; j++)
                if (str[i] == str[j])
                    res = Math.max(res,
                         Math.abs(j - i - 1));

        return res;
    }

    // Driver code
    let str = "abba";
    document.write(maximumChars(str));


// This code is contributed by unknown2108
</script>

Output:

2

Time Complexity : O(n^2)

Auxiliary Space: O(1),  since no extra space has been taken.

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

Javascript

<script>
    // Efficient javascript program to find maximum
    // number of characters between two
    // occurrences of same character

    let MAX_CHAR = 256;

    function maximumChars(str)
    {
        let n = str.length;
        let res = -1;

        // Initialize all indexes as -1.
        let firstInd = new Array(MAX_CHAR);

        for (let i = 0; i < MAX_CHAR; i++)
            firstInd[i] = -1;

        for (let i = 0; i < n; i++)
        {
           let first_ind = firstInd[str[i].charCodeAt(0)];

            // If this is first occurrence
            if (first_ind == -1)
                firstInd[str[i].charCodeAt(0)] = 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
    let str = "abba";
    document.write(maximumChars(str));


// This code is contributed by patel2127
</script>

Output:  

2

Time Complexity : O(n)

Auxiliary Space: O(256) since 256 extra space has been taken.

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