sorting array of 1’s and 0’s in O(n)

keep left and right pointer.

increment left till you encounter 1 as you move along left pointer.(left to right)

Similarly decrement right till you encounter 0 as you move along right pointer.(right to left)

if left < right

swap the elements

and continue from the top if left pointer < right pointer

[gist https://gist.github.com/vishnujayvel/ad165150acce269c4690 ]