Sort Colors

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:

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?

class Solution {
    public void sortColors(int[] nums) {
        if(nums == null || nums.length == 0) return;
        
        int pl = 0, ph = nums.length -1;
        
        int i = 0;
        
        while(i <= ph){
            if(nums[i] == 0){
                swap(nums,i,pl);
                i++;
                pl++;
            }
            else if(nums[i] == 1){
                i++;
            }
            else{
                swap(nums,i,ph);
                ph--;
            }
        }
    }
    
    public void swap(int[] nums, int x, int y){
        int tmp = nums[x];
        nums[x] = nums[y];
        nums[y] = tmp;
    }
}