75. Sort Colors
Contents
Problem
Given an array with n objects colored red, white or blue, sort them inplace so that objects of the same color are adjacent, with the colors in the order red, white and blue.
Here, we will use the integers 0, 1, and 2 to represent the color red, white, and blue respectively.
Note: You are not suppose to use the library’s sort function for this problem.
example 1


Follow up:
 A rather straight forward solution is a twopass algorithm using counting sort. First, iterate the array counting number of 0’s, 1’s, and 2’s, then overwrite array with total number of 0’s, then 1’s and followed by 2’s.
 Could you come up with a onepass algorithm using only constant space?
Solution
In place sort
Main idea is use two pointers: end of zero sequence
, and end of one sequene
.
Walk throw array and check if current element in zero – swap it with next element of end of zero sequence
. If current element is one – swap in with next element of end of one sequene
.

