# Segregate 0s and 1s in an array

Hello Everyone,

You are 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.

Input array = [0, 1, 0, 1, 0, 0, 1, 1, 1, 0]
Output array = [0, 0, 0, 0, 0, 1, 1, 1, 1, 1]

Method (Count 0s or 1s)

1. Count the number of 0s. Let count be C.
2. Once we have count, we can put C 0s at the beginning and 1s at the remaining n – C positions in array.
Time Complexity : O(n)

`// C++ code to Segregate 0s and 1s in an array`

`#include <bits/stdc++.h>`

`using` `namespace` `std;`

`// Function to segregate 0s and 1s`

`void` `segregate0and1(` `int` `arr[], ` `int` `n)`

`{`

` ` `int` `count = 0; ` `// Counts the no of zeros in arr`

` ` `for` `(` `int` `i = 0; i < n; i++) {`

` ` `if` `(arr[i] == 0)`

` ` `count++;`

` ` `}`

` ` `// Loop fills the arr with 0 until count`

` ` `for` `(` `int` `i = 0; i < count; i++)`

` ` `arr[i] = 0;`

` ` `// Loop fills remaining arr space with 1`

` ` `for` `(` `int` `i = count; i < n; i++)`

` ` `arr[i] = 1;`

`}`

`// Function to print segregated array`

`void` `print(` `int` `arr[], ` `int` `n)`

`{`

` ` `cout << ` `"Array after segregation is "` `;`

` ` `for` `(` `int` `i = 0; i < n; i++)`

` ` `cout << arr[i] << ` `" "` `;`

`}`

`// Driver function`

`int` `main()`

`{`

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

` ` `int` `n = ` `sizeof` `(arr) / ` `sizeof` `(arr[0]);`

` `

` ` `segregate0and1(arr, n);`

` ` `print(arr, n);`

` `

` ` `return` `0;`

`}`

Output :

Array after segregation is 0 0 1 1 1 1