Make all characters in given string equal by changing vowel into consonant and vice versa

Given a string str containing lowercase characters, the task is to find the minimum number of operations needed to make all the characters equal. In one operation, any consonant can be converted to any vowel or any vowel can be converted to any consonant.

Examples:

Input: str = “banana”
Output: 3
Explanation: Convert all consonants to Vowel character A

Input: str = “hexon”
Output: 5
Explanation: Convert E to O first then all the consonants to Alphabet O

Approach: The basic catch here is that:

• The operations required to change a consonant to another consonant or a vowel to another vowel: 2 Operation
• The operation required to change a consonant to a vowel or a vowel to consonant: 1 Operation

So, it’s clear that it is more economical to change a consonant to a vowel or a vowel to a consonant than changing a consonant to another consonant or a vowel to another vowel.

Now to solve this question, follow the steps below:

1. Calculate the frequency of all the characters and find the consonant and vowels with the highest frequency, let’s say A and B respectively.
2. Try to change all the characters to A and B, and store the operations required in variables minA and minB respectively.
3. Minimum of minA and minB is the answer to this problem.

Below is the implementation of the above approach.

C++

// C++ program for the above approach

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

// Function to return the minimum operations
// required to make all string characters equal
int minOperations(string str)
{
    int n = str.size();

    // Vector to store the
    // frequency of all characters
    vector<int> freq(26, 0);

    for (auto x : str) {
        freq[x - 'a']++;
    }

    int mxA = INT_MIN, mxB = INT_MIN;

    // Variables to store
    // consonant and vowel
    // with highest frequency
    char A, B;

    vector<char> vowels
        = { 'a', 'e', 'i', 'o', 'u' };

    for (int i = 0; i < 26; ++i) {
        bool isVowel = 0;
        for (auto x : vowels) {
            if ('a' + i == x) {
                isVowel = 1;
                break;
            }
        }

        // If current character is a vowel
        if (isVowel) {
            if (mxB < freq[i]) {
                mxB = freq[i];
                B = 'a' + i;
            }
        }

        // If current character is a consonant
        else {
            if (mxA < freq[i]) {
                mxA = freq[i];
                A = 'a' + i;
            }
        }
    }

    int minA = 0, minB = 0;
    for (auto x : str) {
        bool isVowel = 0;
        for (auto y : vowels) {
            if (x == y) {
                isVowel = 1;
                break;
            }
        }

        // If current character is a vowel
        if (isVowel) {
            if (x != B) {
                minB += 2;
            }
            minA += 1;
        }

        // If current character is a
        // consonant
        else {
            if (x != A) {
                minA += 2;
            }
            minB += 1;
        }
    }

    // If no vowel exists
    if (mxB == INT_MIN) {
        return minA;
    }

    // If no consonant exists
    if (mxA == INT_MIN) {
        return minB;
    }

    // Returning minimum of the two
    return min(minA, minB);
}

// Driver Code
int main()
{
    string str = "hexon";
    cout << minOperations(str);
}

Java

// Java program for the above approach
import java.util.*;
public class GFG {

    // Function to return the minimum operations
    // required to make all string characters equal
    static int minOperations(String str)
    {
        int n = str.length();

        // Vector to store the
        // frequency of all characters
        char[] freq = new char[26];

        for(char x : str.toCharArray()) { freq[x - 'a']++; }

        int mxA = Integer.MIN_VALUE, mxB = Integer.MIN_VALUE;

        // Variables to store
        // consonant and vowel
        // with highest frequency
        char A = ' ', B = ' ';

        char[] vowels = { 'a', 'e', 'i', 'o', 'u' };

        for (int i = 0; i < 26; ++i) {
            int isVowel = 0;
            for(char x : vowels)
            {
                if ('a' + i == x) {
                    isVowel = 1;
                    break;
                }
            }

            // If current character is a vowel
            if (isVowel > 0) {
                if (mxB < freq[i]) {
                    mxB = freq[i];
                    B = (char)(97 + i);
                }
            }

            // If current character is a consonant
            else {
                if (mxA < freq[i]) {
                    mxA = freq[i];
                    A = (char)(97 + i);
                }
            }
        }

        int minA = 0, minB = 0;
        for(char x : str.toCharArray())
        {
            int isVowel = 0;
            for(char y : vowels)
            {
                if (x == y) {
                    isVowel = 1;
                    break;
                }
            }

            // If current character is a vowel
            if (isVowel > 0) {
                if (x != B) {
                    minB += 2;
                }
                minA += 1;
            }

            // If current character is a
            // consonant
            else {
                if (x != A) {
                    minA += 2;
                }
                minB += 1;
            }
        }

        // If no vowel exists
        if (mxB == Integer.MIN_VALUE) {
            return minA;
        }

        // If no consonant exists
        if (mxA == Integer.MIN_VALUE) {
            return minB;
        }

        // Returning minimum of the two
        return Math.min(minA, minB);
    }

    // Driver Code
    public static void main(String args[])
    {
        String str = "hexon";
        System.out.println(minOperations(str));
    }
}

// This code is contributed by Samim Hossain Mondal.

Python3

# python program for the above approach
INT_MIN = -2147483647 - 1

# Function to return the minimum operations
# required to make all string characters equal
def minOperations(str):

    n = len(str)

    # Vector to store the
    # frequency of all characters
    freq = [0 for _ in range(26)]

    for x in str:
        freq[ord(x) - ord('a')] += 1

    mxA = INT_MIN
    mxB = INT_MIN

    # Variables to store
    # consonant and vowel
    # with highest frequency
    A = ''
    B = ''

    vowels = ['a', 'e', 'i', 'o', 'u']

    for i in range(0, 26):
        isVowel = 0

        for x in vowels:
            if (ord('a') + i == ord(x)):
                isVowel = 1
                break

        # If current character is a vowel
        if (isVowel):
            if (mxB < freq[i]):
                mxB = freq[i]
                B = chr(ord('a') + i)

        # If current character is a consonant
        else:
            if (mxA < freq[i]):
                mxA = freq[i]
                A = chr(ord('a') + i)

    minA = 0
    minB = 0
    for x in str:
        isVowel = 0
        for y in vowels:
            if (x == y):
                isVowel = 1
                break

        # If current character is a vowel
        if (isVowel):
            if (x != B):
                minB += 2
            minA += 1

            # If current character is a
            # consonant
        else:
            if (x != A):
                minA += 2
            minB += 1

        # If no vowel exists
    if (mxB == INT_MIN):
        return minA

        # If no consonant exists
    if (mxA == INT_MIN):
        return minB

        # Returning minimum of the two
    return min(minA, minB)

# Driver Code
if __name__ == "__main__":

    str = "hexon"
    print(minOperations(str))

    # This code is contributed by rakeshsahni

C#

// C# program for the above approach
using System;
class GFG {

    // Function to return the minimum operations
    // required to make all string characters equal
    static int minOperations(string str)
    {
        int n = str.Length;

        // Vector to store the
        // frequency of all characters
        char[] freq = new char[26];

        foreach(char x in str) { freq[x - 'a']++; }

        int mxA = Int32.MinValue, mxB = Int32.MinValue;

        // Variables to store
        // consonant and vowel
        // with highest frequency
        char A = ' ', B = ' ';

        char[] vowels = { 'a', 'e', 'i', 'o', 'u' };

        for (int i = 0; i < 26; ++i) {
            int isVowel = 0;
            foreach(char x in vowels)
            {
                if ('a' + i == x) {
                    isVowel = 1;
                    break;
                }
            }

            // If current character is a vowel
            if (isVowel > 0) {
                if (mxB < freq[i]) {
                    mxB = freq[i];
                    B = (char)(97 + i);
                }
            }

            // If current character is a consonant
            else {
                if (mxA < freq[i]) {
                    mxA = freq[i];
                    A = (char)(97 + i);
                }
            }
        }

        int minA = 0, minB = 0;
        foreach(char x in str)
        {
            int isVowel = 0;
            foreach(char y in vowels)
            {
                if (x == y) {
                    isVowel = 1;
                    break;
                }
            }

            // If current character is a vowel
            if (isVowel > 0) {
                if (x != B) {
                    minB += 2;
                }
                minA += 1;
            }

            // If current character is a
            // consonant
            else {
                if (x != A) {
                    minA += 2;
                }
                minB += 1;
            }
        }

        // If no vowel exists
        if (mxB == Int32.MinValue) {
            return minA;
        }

        // If no consonant exists
        if (mxA == Int32.MinValue) {
            return minB;
        }

        // Returning minimum of the two
        return Math.Min(minA, minB);
    }

    // Driver Code
    public static void Main()
    {
        string str = "hexon";
        Console.WriteLine(minOperations(str));
    }
}

// This code is contributed by ukasp.

Javascript

<script>
// Javascript program for the above approach

// Function to return the minimum operations
// required to make all string characters equal
function minOperations(str) {
  let n = str.length;

  // Vector to store the
  // frequency of all characters
  let freq = new Array(26).fill(0);

  for (x of str) {
    freq[x.charCodeAt(0) - 'a'.charCodeAt(0)]++;
  }

  let mxA = Number.MIN_SAFE_INTEGER, mxB = Number.MIN_SAFE_INTEGER;

  // Variables to store
  // consonant and vowel
  // with highest frequency
  let A = "", B = "";

  let vowels = ['a', 'e', 'i', 'o', 'u'];

  for (let i = 0; i < 26; ++i) {
    let isVowel = 0;
    for (x of vowels) {
      if ('a'.charCodeAt(0) + i == x.charCodeAt(0)) {
        isVowel = 1;
        break;
      }
    }

    // If current character is a vowel
    if (isVowel) {
      if (mxB < freq[i]) {
        mxB = freq[i];
        B = String.fromCharCode('a'.charCodeAt(0) + i);
      }
    }

    // If current character is a consonant
    else {
      if (mxA < freq[i]) {
        mxA = freq[i];
        A = String.fromCharCode('a'.charCodeAt(0) + i);
      }
    }
  }

  let minA = 0, minB = 0;
  for (x of str) {
    let isVowel = 0;
    for (y of vowels) {
      if (x == y) {
        isVowel = 1;
        break;
      }
    }

    // If current character is a vowel
    if (isVowel) {
      if (x != B) {
        minB += 2;
      }
      minA += 1;
    }

    // If current character is a
    // consonant
    else {
      if (x != A) {
        minA += 2;
      }
      minB += 1;
    }
  }

  // If no vowel exists
  if (mxB == Number.MIN_SAFE_INTEGER) {
    return minA;
  }

  // If no consonant exists
  if (mxA == Number.MIN_SAFE_INTEGER) {
    return minB;
  }

  // Returning minimum of the two
  return Math.min(minA, minB);
}

// Driver Code

let str = "hexon";
document.write(minOperations(str))

// This code is contributed by saurabh_jaiswal.
</script>

Output

5

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

Another Approach:

1. Iterate over each character in the input string and count the number of vowels and consonants separately.
2. If either the vowel count or consonant count is zero, return 0 because all characters are already equal.
3. If the vowel count and consonant count are equal, return either count since any character can be converted to the other.
4. Otherwise, return the minimum of the vowel count and consonant count multiplied by 2, plus 1 to account for the remaining characters that need to be converted to the opposite type.
5. This minimum count represents the minimum number of operations needed to make all characters in the string equal.

Below is the implementation of the above approach:

C++

#include <iostream>
#include <string>
#include <algorithm>

bool isVowel(char c) {
    c = tolower(c);
    return (c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u');
}

int minOperationsToMakeAllCharactersEqual(const std::string& str) {
    int vowelCount = 0;
    int consonantCount = 0;

    for (char c : str) {
        if (isVowel(c)) {
            vowelCount++;
        } else {
            consonantCount++;
        }
    }

    if (vowelCount == 0 || consonantCount == 0) {
        return 0; // All characters are already equal
    }

    if (vowelCount == consonantCount) {
        return vowelCount; // Both vowels and consonants are equal, any character can be converted to the other
    }

    return std::min(vowelCount, consonantCount) * 2 + 1;
}

int main() {
    std::string str = "hexon";
    int minOperations = minOperationsToMakeAllCharactersEqual(str);
    std::cout << minOperations << std::endl;

    return 0;
}
// This code is contributed by rudra1807raj

Java

//Java program to implement above approach
import java.util.HashSet;

public class Main {

    // Function to check if a character is a vowel
    private static boolean isVowel(char c) {
        c = Character.toLowerCase(c);
        // Using HashSet to efficiently check if the character is a vowel
        HashSet<Character> vowels = new HashSet<>();
        vowels.add('a');
        vowels.add('e');
        vowels.add('i');
        vowels.add('o');
        vowels.add('u');
        return vowels.contains(c);
    }

    // Function to calculate the minimum number of operations
    // to make all characters in the string equal
    private static int minOperationsToMakeAllCharactersEqual(String string) {
        int vowelCount = 0;
        int consonantCount = 0;

        // Counting the number of vowels and consonants in the string
        for (char c : string.toCharArray()) {
            if (isVowel(c)) {
                vowelCount++;
            } else {
                consonantCount++;
            }
        }

        // All characters are already equal (either all vowels or all consonants)
        if (vowelCount == 0 || consonantCount == 0) {
            return 0;
        }

        // Both vowels and consonants are equal, any character can be converted to the other
        if (vowelCount == consonantCount) {
            return vowelCount;
        }

        // Return the minimum of vowelCount and consonantCount multiplied by 2 plus 1
        return Math.min(vowelCount, consonantCount) * 2 + 1;
    }

    // Driver code
    public static void main(String[] args) {
        String string = "hexon";
        int minOperations = minOperationsToMakeAllCharactersEqual(string);
        System.out.println(minOperations);
    }
}

Python3

# Python3 program for the above approach
def is_vowel(c):
    c = c.lower()
    return c in ['a', 'e', 'i', 'o', 'u']

def min_operations_to_make_all_characters_equal(string):
    vowel_count = 0
    consonant_count = 0

    for c in string:
        if is_vowel(c):
            vowel_count += 1
        else:
            consonant_count += 1

    if vowel_count == 0 or consonant_count == 0:
        return 0  # All characters are already equal

    if vowel_count == consonant_count:
        return vowel_count  # Both vowels and consonants are equal, any character can be converted to the other

    return min(vowel_count, consonant_count) * 2 + 1

# Driver code
if __name__ == '__main__':
    string = "hexon"
    min_operations = min_operations_to_make_all_characters_equal(string)
    print(min_operations)

C#

//C# code for the above approach
using System;

class Program
{
    // Function to check if a character is a vowel
    static bool IsVowel(char c)
    {
        c = char.ToLower(c);
        return (c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u');
    }

    // Function to calculate the minimum operations needed to make all characters equal
    static int MinOperationsToMakeAllCharactersEqual(string str)
    {
        int vowelCount = 0;
        int consonantCount = 0;

        foreach (char c in str)
        {
            if (IsVowel(c))
            {
                vowelCount++;
            }
            else
            {
                consonantCount++;
            }
        }

        if (vowelCount == 0 || consonantCount == 0)
        {
            return 0; // All characters are already equal
        }

        if (vowelCount == consonantCount)
        {
            return vowelCount; // Both vowels and consonants are equal, any character can be converted to the other
        }

        return Math.Min(vowelCount, consonantCount) * 2 + 1;
    }

    static void Main()
    {
        string str = "hexon";
        int minOperations = MinOperationsToMakeAllCharactersEqual(str);
        Console.WriteLine(minOperations);
    }
}

Javascript

//Javascript program to implement above approach

// Function to check if a character is a vowel
function isVowel(c) {
    c = c.toLowerCase();
    return (c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u');
}

// Function to calculate the minimum number of operations
// to make all characters in the string equal
function minOperationsToMakeAllCharactersEqual(str) {
    let vowelCount = 0;
    let consonantCount = 0;

// Counting the number of vowels and consonants in the string
    for (let c of str) {
        if (isVowel(c)) {
            vowelCount++;
        } else {
            consonantCount++;
        }
    }
// All characters are already equal (either all vowels or all consonants)
    if (vowelCount == 0 || consonantCount == 0) {
        return 0; // All characters are already equal
    }
// Both vowels and consonants are equal, any character can be converted to the other
    if (vowelCount == consonantCount) {
        return vowelCount; // Both vowels and consonants are equal, any character can be converted to the other
    }

    return Math.min(vowelCount, consonantCount) * 2 + 1;
}

let str = "hexon";
let minOperations = minOperationsToMakeAllCharactersEqual(str);
console.log(minOperations);

Output

5

Time Complexity: O(N).
Auxiliary Space: O(1).