An array contains only records with a component that contains only1 or 2. Specify an algorithm that sorts the array by this componentin situ with running time O(n). Is there an algorithm that sorts...

An array contains only records with a component that contains only
1 or 2. Specify an algorithm that sorts the array by this component
in situ with running time O(n). Is there an algorithm that sorts the
array in situ with running time O(n) if elements 1, 2 and 3 occur?