Largest index for each distinct character in given string with frequency K

Last Updated : 29 Dec, 2022

Given a string S consisting of lowercase English letters and an integer K, the task is to find, for each distinct character in S, the largest index having this character exactly K times. If no such characters exist, print -1. Print the result in a lexicographical ordering.
Note: Consider 0-based indexing in S.

Examples:

Input: S = "cbaabaacbcd", K = 2
Output: { {a 4}, {b 7}, {c 8} }
Explanation:
For 'a', the largest index having 2 a's is "cbaab".
For 'b', the largest index having 2 b's is "cbaabaac".
For 'c', the largest index having 2 c's is "cbaabaacb".
For 'd', the is no index up to which we have 2 d's

Input: P = "acbacbacbaba", K = 3
Output: { {a 8}, {b 9}, {c 11} }

Approach: The idea is to first find all the distinct characters in string S. Then for each lowercase English character, check whether it is present in S or not and run a for loop from the beginning of S and maintain the count of that character that occurred till now. When the count becomes equal to K update the index answer accordingly. Finally, append this character and its corresponding index in the vector result.

Below is the implementation of the above approach.

C++

// C++ implementation of the approach

#include <bits/stdc++.h>
using namespace std;

// Function to find largest index for each
// distinct character occurring exactly K times.
void maxSubstring(string& S, int K, int N)
{

    // finding all characters present in S
    int freq[26];
    memset(freq, 0, sizeof freq);

    // Finding all distinct characters in S
    for (int i = 0; i < N; ++i) {
        freq[S[i] - 'a'] = 1;
    }

    // vector to store result for each character
    vector<pair<char, int> > answer;

    // loop through each lower case English character
    for (int i = 0; i < 26; ++i) {

        // if current character is absent in s
        if (freq[i] == 0)
            continue;

        // getting current character
        char ch = i + 97;

        // finding count of character ch in S
        int count = 0;

        // to store max Index encountred so far
        int index = -1;

        for (int j = 0; j < N; ++j) {
            if (S[j] == ch)
                count++;

            if (count == K)
                index = j;
        }

        answer.push_back({ ch, index });
    }

    int flag = 0;

    // printing required result
    for (int i = 0; i < (int)answer.size(); ++i) {

        if (answer[i].second > -1) {
            flag = 1;
            cout << answer[i].first << " "
                << answer[i].second << endl;
        }
    }

    // If no such character exists, print -1
    if (flag == 0)
        cout << "-1" << endl;
}

// Driver code
int main()
{
    string S = "cbaabaacbcd";
    int K = 2;
    int N = S.length();

    maxSubstring(S, K, N);

    return 0;
}

Java

// Java implementation of the approach
import java.util.*;
class GFG{
    static class pair
    {     char first;
        int  second; 
        public pair(char first, int second)  
        { 
            this.first = first; 
            this.second = second; 
        }    
} 
  
// Function to find largest
//  index for each distinct 
// character occurring exactly K times.
static void maxSubString(char [] S, 
                         int K, int N)
{
    // finding all characters present in S
    int []freq = new int[26];    

    // Finding all distinct characters in S
    for (int i = 0; i < N; ++i) 
    {
        freq[S[i] - 'a'] = 1;
    }

    // vector to store result for each character
    Vector<pair> answer = new Vector<pair>();

    // loop through each lower case English character
    for (int i = 0; i < 26; ++i) 
    {
        // if current character is absent in s
        if (freq[i] == 0)
            continue;

        // getting current character
        char ch = (char) (i + 97);

        // finding count of character ch in S
        int count = 0;

        // to store max Index encountred so far
        int index = -1;

        for (int j = 0; j < N; ++j) 
        {
            if (S[j] == ch)
                count++;
            if (count == K)
                index = j;
        }
        answer.add(new pair(ch, index ));
    }

    int flag = 0;

    // printing required result
    for (int i = 0; i < (int)answer.size(); ++i) 
    {
        if (answer.get(i).second > -1) 
        {
            flag = 1;
            System.out.print(answer.get(i).first + " " + 
                             answer.get(i).second + "\n");
        }
    }

    // If no such character exists, print -1
    if (flag == 0)
        System.out.print("-1" + "\n");
}

// Driver code
public static void main(String[] args)
{
    String S = "cbaabaacbcd";
    int K = 2;
    int N = S.length();
    maxSubString(S.toCharArray(), K, N);
}
}

// This code is contributed by shikhasingrajput

Python3

# Python3 implementation of the approach
# Function to find largest index for each
# distinct character occurring exactly K times.
def maxSubstring(S, K, N):
    
    # Finding all characters present in S
    freq = [0 for i in range(26)]
    
    # Finding all distinct characters in S
    for i in range(N):
        freq[ord(S[i]) - 97] = 1

    # To store result for each character
    answer = []

    # Loop through each lower 
    # case English character
    for i in range(26):
        
        # If current character is absent in s
        if (freq[i] == 0):
            continue

        # Getting current character
        ch = chr(i + 97)

        # Finding count of character ch in S
        count = 0

        # To store max Index encountred so far
        index = -1

        for j in range(N):
            if (S[j] == ch):
                count += 1

            if (count == K):
                index = j

        answer.append([ch, index])

    flag = 0

    # Printing required result
    for i in range(len(answer)):
        if (answer[i][1] > -1):
            flag = 1
            print(answer[i][0],
                  answer[i][1])

    # If no such character exists,
    # print -1
    if (flag == 0):
        print("-1")

# Driver code
if __name__ == '__main__':
    
    S = "cbaabaacbcd"
    K = 2
    N = len(S)

    maxSubstring(S, K, N)

# This code is contributed by Surendra_Gangwar

// C# implementation of the approach
using System;
using System.Collections.Generic;

class GFG{
    
class pair
{     
    public char first;
    public int second; 
    
    public pair(char first, int second) 
    { 
        this.first = first; 
        this.second = second; 
    } 
} 

// Function to find largest
// index for each distinct 
// character occurring exactly K times.
static void maxSubString(char [] S, 
                         int K, int N)
{
    
    // Finding all characters present in S
    int []freq = new int[26]; 

    // Finding all distinct characters in S
    for(int i = 0; i < N; ++i) 
    {
        freq[S[i] - 'a'] = 1;
    }

    // To store result for each character
    List<pair> answer = new List<pair>();

    // Loop through each lower case
    // English character
    for(int i = 0; i < 26; ++i) 
    {
        
        // If current character is absent in s
        if (freq[i] == 0)
            continue;

        // Getting current character
        char ch = (char)(i + 97);

        // Finding count of character ch in S
        int count = 0;

        // To store max Index encountred so far
        int index = -1;

        for(int j = 0; j < N; ++j) 
        {
            if (S[j] == ch)
                count++;
            if (count == K)
                index = j;
        }
        answer.Add(new pair(ch, index));
    }

    int flag = 0;

    // Printing required result
    for(int i = 0; i < (int)answer.Count; ++i) 
    {
        if (answer[i].second > -1) 
        {
            flag = 1;
            Console.Write(answer[i].first + " " + 
                          answer[i].second + "\n");
        }
    }

    // If no such character exists, print -1
    if (flag == 0)
        Console.Write("-1" + "\n");
}

// Driver code
public static void Main(String[] args)
{
    String S = "cbaabaacbcd";
    int K = 2;
    int N = S.Length;
    
    maxSubString(S.ToCharArray(), K, N);
}
}

// This code is contributed by Amit Katiyar

JavaScript

<script>
      // JavaScript implementation of the approach
      // Function to find largest
      // index for each distinct
      // character occurring exactly K times.
      function maxSubString(S, K, N) {
        // Finding all characters present in S
        var freq = new Array(26).fill(0);

        // Finding all distinct characters in S
        for (var i = 0; i < N; ++i) {
          freq[S[i].charCodeAt(0) - "a".charCodeAt(0)] = 1;
        }

        // To store result for each character
        var answer = [];

        // Loop through each lower case
        // English character
        for (var i = 0; i < 26; ++i) {
          // If current character is absent in s
          if (freq[i] === 0) 
              continue;

          // Getting current character
          var ch = String.fromCharCode(i + 97);

          // Finding count of character ch in S
          var count = 0;

          // To store max Index encountred so far
          var index = -1;

          for (var j = 0; j < N; ++j) {
            if (S[j] === ch) count++;
            if (count === K) index = j;
          }
          answer.push([ch, index]);
        }

        var flag = 0;

        // Printing required result
        for (var i = 0; i < answer.length; ++i) {
          if (answer[i][1] > -1) {
            flag = 1;
            document.write(answer[i][0] + " " + answer[i][1] + "<br>");
          }
        }

        // If no such character exists, print -1
        if (flag === 0) 
            document.write("-1" + "<br>");
      }

      // Driver code
      var S = "cbaabaacbcd";
      var K = 2;
      var N = S.length;

      maxSubString(S.split(""), K, N);
</script>

Output:

a 4
b 7
c 8

Time Complexity: O(26 * N)
Auxiliary Space: O(1)

Count of substrings of given string with frequency of each character at most K

Sanjit_Prasad

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