Sort a binary array in linear time.

To sort a binary array (containing only 0s and 1s) in linear time, you can use a two-pointer approach or a counting approach.

Counting Approach:

1. Count the number of 0s and 1s in the array.
2. Create a new array or overwrite the original array by placing all the 0s first, followed by all the 1s, based on the counts.

Two-Pointer Approach:

1. Initialize two pointers, left at the beginning of the array and right at the end.
2. Iterate while left is less than right:
   • If array[left] is 1 and array[right] is 0, swap them. Then increment left and decrement right.
   • If array[left] is 0, increment left.
   • If array[right] is 1, decrement right.

Both methods achieve sorting in O(n) time complexity, where n is the size of the array, as they involve a single pass or a constant number of passes through the array.