Sort Colors II

Problem

Given an array of n objects with k different colors (numbered from 1 to k), sort them so that objects of the same color are adjacent, with the colors in the order 1, 2, ... k.

Note

You are not suppose to use the library's sort function for this problem.

Example

Given colors = [3, 2, 2, 1, 4], k = 4, your code should sort colors in-place to [1, 2, 2, 3, 4].