Sort an array containing two types of elements

Given an array of 0s and 1s in random order. Segregate 0s on left side and 1s on right side of the array. Traverse array only once.

Examples:

Input :  arr[] = [0, 1, 0, 1, 0, 0, 1, 1, 1, 0] 
Output : arr[] = [0, 0, 0, 0, 0, 1, 1, 1, 1, 1] 

Input :  arr[] = [1, 1, 1, 0, 1, 0, 0, 1, 1, 1, 1] 
Output : arr[] = [0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1] 

We have already discussed a solution Segregate 0s and 1s in an array

In this post, a new solution is discussed. 

• Step 1 : Here we can take two pointers type0 (for element 0) starting from beginning (index = 0) and type1 (for element 1) starting from end index.
• Step 2: We intend to put 1 to the right side of the array. Once we have done this then 0 will definitely towards left side of array to achieve this we do following. 

We compare elements at index type0 

1. if this is 1 then this should be moved to right side so we need to swap this with index type1 once swapped we are sure that element at index type1 is ‘1’ so we need to decrement index type1 
2. else it will be 0 then we need to simple increment index type0

Implementation:

C++14

// CPP program to sort an array with two types
// of values in one traversal.
#include <bits/stdc++.h>
using namespace std;

/* Method for segregation 0 and 1 given
   input array */
void segregate0and1(int arr[], int n)
{
    int type0 = 0;
    int type1 = n - 1;

    while (type0 < type1) {
        if (arr[type0] == 1) {
            swap(arr[type0], arr[type1]);
            type1--;
        }
        else {
            type0++;
        }
    }
}

// Driver program
int main()
{
    int arr[] = { 1, 1, 1, 0, 1, 0, 0, 1, 1, 1, 1 };
    int n = sizeof(arr)/sizeof(arr[0]);
    segregate0and1(arr, n);
    for (int a : arr)
        cout << a << " ";
}

Java

// Java program to sort an array with two types
// of values in one traversal.public class GFG {
/* Method for segregation 0 and 1
     given input array */
class segregation {
    static void segregate0and1(int arr[], int n)
    {
        int type0 = 0;
        int type1 = n - 1;

        while (type0 < type1) {
            if (arr[type0] == 1) {

                // swap type0 and type1
                arr[type0] = arr[type0] + arr[type1];
                arr[type1] = arr[type0] - arr[type1];
                arr[type0] = arr[type0] - arr[type1];
                type1--;
            }
            else {
                type0++;
            }
        }
    }

    // Driver program
    public static void main(String[] args)
    {
        int arr[]
            = { 1, 1, 1, 0, 1, 0, 0, 1, 1, 1, 1, 1, 0, 0 };

        segregate0and1(arr, arr.length);
        for (int a : arr)
            System.out.print(a + " ");
    }
}

Python3

# Python3 program to sort an array with
# two types of values in one traversal.

# Method for segregation 0 and
# 1 given input array
def segregate0and1(arr, n):

    type0 = 0; type1 = n - 1

    while (type0 < type1):
        if (arr[type0] == 1):
            arr[type0], arr[type1] = arr[type1], arr[type0]
            type1 -= 1

        else:
            type0 += 1

# Driver Code
arr = [1, 1, 1, 0, 1, 0, 0, 1, 1, 1, 1]
n = len(arr)
segregate0and1(arr, n)
for i in range(0, n):
    print(arr[i], end = " ")

# This code is contributed by Smitha Dinesh Semwal

C#

// C# program to sort an array with two types
// of values in one traversal.
using System;

class GFG {

    static void segregate0and1(int []arr, int n)
    {
        int type0 = 0;
        int type1 = n - 1;

        while (type0 < type1)
        {

            if (arr[type0] == 1)
            {

                // swap type0 and type1
                arr[type0] = arr[type0] + arr[type1];
                arr[type1] = arr[type0]-arr[type1];
                arr[type0] = arr[type0]-arr[type1];
                type1--;
            }
            else {
                type0++;
            }
        }
    }

    // Driver program
    public static void Main()
    {

        int []arr = { 1, 1, 1, 0, 1, 0, 0,
                             1, 1, 1, 1 };

        segregate0and1(arr, arr.Length);

        for (int i = 0; i < arr.Length; i++)
            Console.Write(arr[i] + " ");
    }
}

// This code is contributed by vt_m.

PHP

<?php
// PHP program to sort an array with two
// types of values in one traversal.

/* Method for segregation 0 and 1
given input array */
function segregate0and1($arr, $n)
{
    $type0 = 0;
    $type1 = $n - 1;

    while ($type0 < $type1)
    {
        if ($arr[$type0] == 1)
        {
            $temp = $arr[$type0];
            $arr[$type0] = $arr[$type1];
            $arr[$type1] = $temp;

            $type1--;
        }
        else
        {
            $type0++;
        }
    }
    return $arr;
}

// Driver Code
$arr = array( 1, 1, 1, 0, 1, 0,
                 0, 1, 1, 1, 1 );
$n = count($arr);
$arr1 = segregate0and1($arr, $n);
for($i = 0; $i < $n ; $i++ )
echo $arr1[$i] . " ";

// This code is contributed by Rajput-Ji
?>

Javascript

<script>

// JavaScript program to sort an array with two types
// of values in one traversal.

    function segregate0and1(arr, n)
    {
        let type0 = 0;
        let type1 = n - 1;

        while (type0 < type1)
        {

            if (arr[type0] == 1)
            {

                // swap type0 and type1
                arr[type0] = arr[type0] + arr[type1];
                arr[type1] = arr[type0]-arr[type1];
                arr[type0] = arr[type0]-arr[type1];
                type1--;
            }
            else {
                type0++;
            }
        }
    }

// Driver Code

    let arr = [1, 1, 1, 0, 1, 0, 0,
                             1, 1, 1, 1 ];

        segregate0and1(arr, arr.length);
        for (let i = 0; i < arr.length; i++)
            document.write(arr[i] + " ");

// This code is contributed by avijitmondal1998.
</script>

Output:

0 0 0 1 1 1 1 1 1 1 1

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

Approach 2:- Using counting sort

Another approach to sort an array containing two types of elements is to use counting sort. Here’s the basic idea:

• Traverse the array and count the number of occurrences of each type of element.
• Create a new array of the same size as the original array.
• Copy the first type of elements into the new array, starting from index 0.
• Copy the second type of elements into the new array, starting from the end of the array.
• The new array is now sorted.

C++

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

/* Method for segregation 0 and 1 given
input array */
void sortTwoTypes(int arr[], int n)
{
    int count[2]
        = { 0 }; // Initialize count of 0s and 1s to 0

    // Count the frequency of 0s and 1s
    for (int i = 0; i < n; i++)
        count[arr[i]]++;

    // Update the original array with sorted elements
    int i = 0;
    for (int j = 0; j < 2; j++) {
        while (count[j]--)
            arr[i++] = j;
    }
}

// Driver program
int main()
{
    int arr[] = { 1, 1, 1, 0, 1, 0, 0, 1, 1, 1, 1 };
    int n = sizeof(arr) / sizeof(arr[0]);
    sortTwoTypes(arr, n);
    for (int a : arr)
        cout << a << " ";
}

Java

import java.util.*;

public class Main {

    /* Method for segregation 0 and 1 given
       input array */
    static void sortTwoTypes(int[] arr, int n)
    {
        int[] count
            = { 0,
                0 }; // Initialize count of 0s and 1s to 0

        // Count the frequency of 0s and 1s
        for (int i = 0; i < n; i++)
            count[arr[i]]++;

        // Update the original array with sorted elements
        int i = 0;
        for (int j = 0; j < 2; j++) {
            while (count[j]-- > 0)
                arr[i++] = j;
        }
    }

    // Driver program
    public static void main(String[] args)
    {
        int[] arr = { 1, 1, 1, 0, 1, 0, 0, 1, 1, 1, 1 };
        int n = arr.length;
        sortTwoTypes(arr, n);
        for (int a : arr)
            System.out.print(a + " ");
    }
}

Python3

def sortTwoTypes(arr, n):
    count = [0, 0]  # Initialize count of 0s and 1s to 0

    # Count the frequency of 0s and 1s
    for i in range(n):
        count[arr[i]] += 1

    # Update the original array with sorted elements
    i = 0
    for j in range(2):
        while count[j] > 0:
            arr[i] = j
            i += 1
            count[j] -= 1


# Driver program
arr = [1, 1, 1, 0, 1, 0, 0, 1, 1, 1, 1]
n = len(arr)
sortTwoTypes(arr, n)
for a in arr:
    print(a, end=" ")

C#

using System;

public class MainClass
{
// Method for segregating 0s and 1s in the input array
static void SortTwoTypes(int[] arr, int n)
{
    int[] count = { 0, 0 }; // Initialize count of 0s and 1s to 0
    // Count the frequency of 0s and 1s
    for (int i = 0; i < n; i++)
        count[arr[i]]++;

    // Update the original array with sorted elements
    int k = 0;
    for (int j = 0; j < 2; j++)
    {
        while (count[j]-- > 0)
            arr[k++] = j;
    }
}

// Driver program
public static void Main(string[] args)
{
    int[] arr = { 1, 1, 1, 0, 1, 0, 0, 1, 1, 1, 1 };
    int n = arr.Length;
    SortTwoTypes(arr, n);
    foreach (int a in arr)
        Console.Write(a + " ");
}
}

Javascript

// JavaScript program for the above approach

function sortTwoTypes(arr, n) {
let count = [0, 0]; // Initialize count of 0s and 1s to 0

// Count the frequency of 0s and 1s
for (let i = 0; i < n; i++) {
count[arr[i]] += 1;
}

// Update the original array with sorted elements
let i = 0;
for (let j = 0; j < 2; j++) {
while (count[j] > 0) {
arr[i] = j;
i += 1;
count[j] -= 1;
}
}
}

// Driver program
let arr = [1, 1, 1, 0, 1, 0, 0, 1, 1, 1, 1];
let n = arr.length;
sortTwoTypes(arr, n); let temp ="";
for (let a of arr) {
temp = temp + a + " ";
} console.log(temp);

Output

0 0 0 1 1 1 1 1 1 1 1 

Time Complexity: O(n), where n is the size of the array
Auxiliary Space: O(1)