Question: Given an array arr[], that contains only 0’s and 1’s. Write a function that separate 0’s and 1’s in the array.
Input: 0, 0, 1, 1, 0, 0, 0, 0, 1, 1, 1, 0, 1, 0, 1
Output: 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1
The objective of the problem is to segregate the array in two parts, and it is more popularly known as a variation of Dutch National Flag Problem.
Method 1:
- The most naive method is to count the number of elements in the given array. Let it be N.
- Do a second scan of the array and count the number of zeroes. Let it be c.
- Now fill the array with c number of 0’s and fill the remaining positions with 1.
Time Complexity:- O(2n)
Method 2:
We can solve this problem in a fashion similar to separating odd and even numbers in an array.
- Initialize 2 indexes, left = 0 and right = size-1.
- Increment left, till it is 0.
- Decrement right till it is 1.
- If (left < right) swap the values at arr[left] and arr[right].
void swap(int *i, int *j)
{
int temp = *i;
*i = *j;
*j = temp;
}
int seperateZeroAndOne(int arr[], int size)
{
// Initialize left and right indexes
int left = 0;
int right = size - 1;
while(left < right)
{
// Increment left index till the number is 0
while(arr[left] == 0 && left < right)
left++;
// Decrement right index till the number is 1
while(arr[right] == 1 && left < right)
right--;
// Time to swap
if(left < right)
{
swap(&arr[left], &arr[right]);
left++;
right--;
}
}
}
Time Complexity:- O(n)