# 75. Sort Colors
# Problem
Given an array with n objects colored red, white or blue, sort them in-place 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
```
Input: [2,0,2,1,1,0]
Output: [0,0,1,1,2,2]
```
## Follow up:
* A rather straight forward solution is a two-pass 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 one-pass 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`.
```go
func sortColors(nums []int) {
ez:=-1
eo:=-1
for idx:=range nums {
if nums[idx] == 0 && ez != idx {
ez++
nums[idx], nums[ez] = nums[ez], nums[idx]
}
if nums[idx] == 1 && eo != idx {
if eo == -1 {
eo = ez
}
eo++
nums[idx], nums[eo] = nums[eo], nums[idx]
}
}
}
```