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# 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 ` `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

 ``

## Javascript

 ``

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 ` `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)

My Personal Notes arrow_drop_up