Sort an Array of 0s, 1s and 2s

Given an array consisting of 0s, 1s, and 2s. Write code to sort an array of 0s, 1s, and 2s without using an extra space or a sorting algorithm.

OR

Given an array of size n containing only 0s, 1s, and 2s. Write a code to sort the array in ascending order.

For example:

Input  : {0, 1, 1, 0, 1, 2, 0, 1, 2}

Output : {0, 0, 0, 1, 1, 1, 1, 2, 2}

In this example, the input array only consists of 0s, 1s, and 2s in an unsorted order.

In the output array, all the 0s, 1s and 2s are in sorted order.