Check if both halves of the string have same set of characters

Difficulty Level : Easy
Last Updated : 14 Jul, 2022

Given a string of lowercase characters only, the task is to check if it is possible to split a string from the middle which will give two halves having the same characters and same frequency of each character. If the length of the given string is ODD then ignore the middle element and check for the rest.

Examples:

Input: abbaab
Output: NO
The two halves contain the same characters
but their frequencies do not match so they
are NOT CORRECT

Input : abccab
Output : YES

Algorithm:
Declare two counter arrays for keeping count of characters in two half of the string, each of size 26.
Now run a loop and take two variables i and j, where i starts from 0 and j starts from (length of string – 1).
For each character in the string, go to the corresponding index in the counter arrays and increment the value by 1 and increment i and decrement j. Do this until i is less than j.
After finishing STEP 3, again run a loop and compare values of counter arrays. If value of first array if not equal to value of second array, then return false.
If all counts matched, return true.

Below is the implementation of above idea:

C++

// C++ program to check if it is
// possible to split string or not
#include <bits/stdc++.h>
using namespace std;
const int MAX_CHAR = 26;
 
// function to check if we can split
// string or not
bool checkCorrectOrNot(string s)
{
    // Counter array initialized with 0
    int count1[MAX_CHAR] = {0};
    int count2[MAX_CHAR] = {0};
 
    // Length of the string
    int n = s.length();
    if (n == 1)
        return true;
 
    // traverse till the middle element
    // is reached
    for (int i=0,j=n-1; i<j; i++,j--)
    {
        // First half
        count1[s[i]-'a']++;
 
        // Second half
        count2[s[j]-'a']++;
    }
 
    // Checking if values are different
    // set flag to 1
    for (int i = 0; i<MAX_CHAR; i++)
        if (count1[i] != count2[i])
            return false;
 
    return true;
}
 
// Driver program to test above function
int main()
{
    // String to be checked
    string s = "abab";
 
    if (checkCorrectOrNot(s))
        cout << "Yes\n";
    else
        cout << "No\n";
    return 0;
}

Java

// Java program to check if it two
// half of string contain same Character
// set or not
public class GFG {
 
    static final int MAX_CHAR = 26;
      
    // function to check both halves
    // for equality
    static boolean checkCorrectOrNot(String s)
    {
        // Counter array initialized with 0
        int[] count1 = new int[MAX_CHAR];
        int[] count2 = new int[MAX_CHAR];
      
        // Length of the string
        int n = s.length();
        if (n == 1)
            return true;
      
        // traverse till the middle element
        // is reached
        for (int i = 0, j = n - 1; i < j; i++, j--)
        {
            // First half
            count1[s.charAt(i) - 'a']++;
      
            // Second half
            count2[s.charAt(j) - 'a']++;
        }
      
        // Checking if values are different
        // set flag to 1
        for (int i = 0; i < MAX_CHAR; i++)
            if (count1[i] != count2[i])
                return false;
      
        return true;
    }
      
    // Driver program to test above function
    public static void main(String args[])
    {
        // String to be checked
        String s = "abab";
      
        if (checkCorrectOrNot(s))
            System.out.println("Yes");
        else
            System.out.println("No");
    }
}
// This code is contributed by Sumit Ghosh

Python3

# Python3 program to check if it is
# possible to split string or not
MAX_CHAR = 26
 
# Function to check if we
# can split string or not
def checkCorrectOrNot(s):
     
    global MAX_CHAR
     
    # Counter array initialized with 0
    count1 = [0] * MAX_CHAR
    count2 = [0] * MAX_CHAR
 
    # Length of the string
    n = len(s)
     
    if n == 1:
        return true
 
    # Traverse till the middle
    # element is reached
    i = 0; j = n - 1
     
    while (i < j):
         
        # First half
        count1[ord(s[i]) - ord('a')] += 1
 
        # Second half
        count2[ord(s[j]) - ord('a')] += 1
 
        i += 1; j -= 1
 
    # Checking if values are
    # different set flag to 1
    for i in range(MAX_CHAR):
         
        if count1[i] != count2[i]:
            return False
             
    return True
 
 
# Driver Code
 
# String to be checked
s = "ababc"
 
print("Yes" if checkCorrectOrNot(s) else "No")
 
 
# This code is contributed by Ansu Kumari.

C#

// C# program to check if it two half of
// string contain same Character set or not
using System;
 
class GFG {
 
    static int MAX_CHAR = 26;
     
    // function to check both halves for
    // equality
    static bool checkCorrectOrNot(string s)
    {
         
        // Counter array initialized with 0
        int []count1 = new int[MAX_CHAR];
        int []count2 = new int[MAX_CHAR];
     
        // Length of the string
        int n = s.Length;
        if (n == 1)
            return true;
     
        // traverse till the middle element
        // is reached
        for (int i = 0, j = n - 1; i < j;
                                   i++, j--)
        {
             
            // First half
            count1[s[i] - 'a']++;
     
            // Second half
            count2[s[j] - 'a']++;
        }
     
        // Checking if values are different
        // set flag to 1
        for (int i = 0; i < MAX_CHAR; i++)
            if (count1[i] != count2[i])
                return false;
     
        return true;
    }
     
    // Driver program to test above function
    public static void Main()
    {
        // String to be checked
        string s = "abab";
     
        if (checkCorrectOrNot(s))
            Console.Write("Yes");
        else
            Console.Write("No");
    }
}
 
// This code is contributed by nitin mittal

PHP

<?php
// PHP program to check if it is
// possible to split string or not
$MAX_CHAR = 26;
 
// function to check if we
// can split string or not
function checkCorrectOrNot($s)
{
    global $MAX_CHAR;
     
    // Counter array initialized with 0
    $count1 = array_fill(0, $MAX_CHAR, NULL);
    $count2 = array_fill(0, $MAX_CHAR, NULL);
 
    // Length of the string
    $n = strlen($s);
    if ($n == 1)
        return true;
 
    // traverse till the middle
    // element is reached
    for ($i = 0, $j = $n - 1;
         $i < $j; $i++, $j--)
    {
        // First half
        $count1[$s[$i] - 'a']++;
 
        // Second half
        $count2[$s[$j] - 'a']++;
    }
 
    // Checking if values are
    // different set flag to 1
    for ($i = 0; $i < $MAX_CHAR; $i++)
        if ($count1[$i] != $count2[$i])
            return false;
 
    return true;
}
 
// Driver Code
 
// String to be checked
$s = "abab";
if (checkCorrectOrNot($s))
    echo "Yes\n";
else
    echo "No\n";
 
// This code is contributed
// by ChitraNayal
?>

Javascript

<script>
// Javascript program to check if it two
// half of string contain same Character
// set or not
     
    let MAX_CHAR = 26;
     
    // function to check both halves
    // for equality
    function checkCorrectOrNot(s)
    {
        // Counter array initialized with 0
        let count1 = new Array(MAX_CHAR);
        let count2 = new Array(MAX_CHAR);
        for(let i=0;i<MAX_CHAR;i++)
        {
            count1[i]=0;
            count2[i]=0;
        }
        
        // Length of the string
        let n = s.length;
        if (n == 1)
            return true;
        
        // traverse till the middle element
        // is reached
        for (let i = 0, j = n - 1; i < j; i++, j--)
        {
            // First half
            count1[s[i] - 'a']++;
        
            // Second half
            count2[s[j] - 'a']++;
        }
        
        // Checking if values are different
        // set flag to 1
        for (let i = 0; i < MAX_CHAR; i++)
            if (count1[i] != count2[i])
                return false;
        
        return true;
    }   
     
    // Driver program to test above function
     
    // String to be checked
    let  s = "abab";
    if (checkCorrectOrNot(s))
        document.write("Yes");
    else
        document.write("No");
     
    //This code is contributed by avanitrachhadiya2155
     
</script>

Output

Yes

Time Complexity : O(n), where n is the length of the string.
Auxiliary Space : O(1)

Space optimized solution:

Below is the space optimized solution of the above approach.
We can solve this problem by using only 1 counter array.
Take a string and increment counts for first half and then decrement counts for second half.
If final counter array is 0, then return true, Else False.

Below is the implementation of above idea:

C++

// C++ program to check if it is
// possible to split string or not
#include <bits/stdc++.h>
using namespace std;
const int MAX_CHAR = 26;
 
// function to check if we can split
// string or not
bool checkCorrectOrNot(string s)
{
    // Counter array initialized with 0
    int count[MAX_CHAR] = {0};
 
    // Length of the string
    int n = s.length();
    if (n == 1)
        return true;
 
    // traverse till the middle element
    // is reached
    for (int i=0,j=n-1; i<j; i++,j--)
    {
        // First half
        count[s[i]-'a']++;
 
        // Second half
        count[s[j]-'a']--;
    }
 
    // Checking if values are different
    // set flag to 1
    for (int i = 0; i<MAX_CHAR; i++)
        if (count[i] != 0)
            return false;
 
    return true;
}
 
// Driver program to test above function
int main()
{
    // String to be checked
    string s = "abab";
 
    if (checkCorrectOrNot(s))
        cout << "Yes\n";
    else
        cout << "No\n";
    return 0;
}

Java

// Java program to check if it two
// half of string contain same Character
// set or not
public class GFG {
 
    static final int MAX_CHAR = 26;
      
    // function to check both halves
    // for equality
    static boolean checkCorrectOrNot(String s)
    {
        // Counter array initialized with 0
        int[] count = new int[MAX_CHAR];
      
        // Length of the string
        int n = s.length();
        if (n == 1)
            return true;
      
        // traverse till the middle element
        // is reached
        for (int i = 0,j = n - 1; i < j; i++, j--)
        {
            // First half
            count[s.charAt(i) - 'a']++;
      
            // Second half
            count[s.charAt(j) - 'a']--;
        }
      
        // Checking if values are different
        // set flag to 1
        for (int i = 0; i < MAX_CHAR; i++)
            if (count[i] != 0)
                return false;
      
        return true;
    }
      
    // Driver program to test above function
    public static void main(String args[])
    {
        // String to be checked
        String s = "abab";
      
        if (checkCorrectOrNot(s))
            System.out.println("Yes");
        else
           System.out.println("No");
    }
}
// This code is contributed by Sumit Ghosh

Python3

# Python3 program to check if it is
# possible to split string or not
MAX_CHAR = 26
 
# Function to check if we 
# can split string or not
def checkCorrectOrNot(s):
     
    global MAX_CHAR
     
    # Counter array initialized with 0
    count = [0] * MAX_CHAR
 
    # Length of the string
    n = len(s)
     
    if n == 1:
        return true
 
    # Traverse till the middle
    # element is reached
    i = 0; j = n-1
     
    while i < j:
         
        # First half
        count[ord(s[i]) - ord('a')] += 1
 
        # Second half
        count[ord(s[j])-ord('a')] -= 1
 
        i += 1; j -= 1
 
    # Checking if values are
    # different, set flag to 1
    for i in range(MAX_CHAR):
         
        if count[i] != 0:
            return False
 
    return True
 
 
# Driver Code
 
# String to be checked
s = "abab"
 
print("Yes" if checkCorrectOrNot(s) else "No")
 
 
# This code is contributed by Ansu Kumari.

C#

// C# program to check if it two
// half of string contain same Character
// set or not
using System;
 
public class GFG {
 
    static int MAX_CHAR = 26;
     
    // function to check both halves
    // for equality
    static bool checkCorrectOrNot(String s)
    {
         
        // Counter array initialized with 0
        int[] count = new int[MAX_CHAR];
     
        // Length of the string
        int n = s.Length;
        if (n == 1)
            return true;
     
        // traverse till the middle element
        // is reached
        for (int i = 0, j = n - 1; i < j; i++, j--)
        {
            // First half
            count[s[i] - 'a']++;
     
            // Second half
            count[s[j] - 'a']--;
        }
     
        // Checking if values are different
        // set flag to 1
        for (int i = 0; i < MAX_CHAR; i++)
            if (count[i] != 0)
                return false;
     
        return true;
    }
     
    // Driver program to test above function
    public static void Main(String []args)
    {
         
        // String to be checked
        String s = "abab";
     
        if (checkCorrectOrNot(s))
            Console.Write("Yes");
        else
            Console.Write("No");
    }
}
 
// This code is contributed by parashar.

PHP

<?PHP
// PHP program to check if it is
// possible to split string or not
$MAX_CHAR = 26;
 
// function to check if we
// can split string or not
function checkCorrectOrNot($s)
{
    global $MAX_CHAR;
     
    // Counter array initialized with 0
    $count = array_fill(0, $MAX_CHAR, NULL);
 
    // Length of the string
    $n = strlen($s);
    if ($n == 1)
        return true;
 
    // traverse till the middle
    // element is reached
    for ($i = 0, $j = $n - 1;
         $i < $j; $i++, $j--)
    {
        // First half
        $count[$s[$i] - 'a']++;
 
        // Second half
        $count[$s[$j] - 'a']--;
    }
 
    // Checking if values are
    // different set flag to 1
    for ($i = 0; $i < $MAX_CHAR; $i++)
        if ($count[$i] != 0)
            return false;
 
    return true;
}
 
// Driver Code
 
// String to be checked
$s = "abab";
if (checkCorrectOrNot($s))
    echo "Yes\n";
else
    echo "No\n";
 
// This code is contributed
// by ChitraNayal
?>

Javascript

<script>
 
// Javascript program to check if it two
// half of string contain same Character
// set or not
     
let MAX_CHAR = 26;
 
// Function to check both halves
// for equality
function checkCorrectOrNot(s)
{
     
    // Counter array initialized with 0
    let count = new Array(MAX_CHAR);
    for(let i = 0; i < count.length; i++)
    {
        count[i] = 0;
    }
   
    // Length of the string
    let n = s.length;
    if (n == 1)
        return true;
   
    // Traverse till the middle element
    // is reached
    for(let i = 0, j = n - 1; i < j; i++, j--)
    {
         
        // First half
        count[s[i] - 'a']++;
   
        // Second half
        count[s[j] - 'a']--;
    }
   
    // Checking if values are different
    // set flag to 1
    for(let i = 0; i < MAX_CHAR; i++)
        if (count[i] != 0)
            return false;
   
    return true;
}
 
// Driver Code
let s = "abab";
 
if (checkCorrectOrNot(s))
    document.write("Yes");
else
    document.write("No");
 
// This code is contributed by rag2127
     
</script>

Output

Yes

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

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