Sort Colors Solutions in Java

/// Source : https://leetcode.com/problems/sort-colors/description/
/// Author : liuyubobobo
/// Time   : 2017-11-13

// Counting
// Time Complexity: O(n)
// Space Complexity: O(3)
public class Solution1 {

    public void sortColors(int[] nums) {

        int[] count = {0, 0, 0};
        for(int i = 0 ; i < nums.length ; i ++){
            assert nums[i] >= 0 && nums[i] <= 2;
            count[nums[i]] ++;
        }

        int index = 0;
        for(int i = 0 ; i < count[0] ; i ++)
            nums[index++] = 0;
        for(int i = 0 ; i < count[1] ; i ++)
            nums[index++] = 1;
        for(int i = 0 ; i < count[2] ; i ++)
            nums[index++] = 2;
    }

    public static void printArr(int[] nums){
        for(int num: nums)
            System.out.print(num + " ");
        System.out.println();
    }

    public static void main(String[] args) {

        int[] nums = {2, 2, 2, 1, 1, 0};
        (new Solution1()).sortColors(nums);
        printArr(nums);
    }
}

/// Source : https://leetcode.com/problems/sort-colors/description/
/// Author : liuyubobobo
/// Time   : 2017-11-13

// Three Way Quick Sort
// Time Complexity: O(n)
// Space Complexity: O(1)
public class Solution2 {

    public void sortColors(int[] nums) {

        int zero = -1;          // [0...zero] == 0
        int two = nums.length;  // [two...n-1] == 2
        for(int i = 0 ; i < two ; ){
            if(nums[i] == 1)
                i ++;
            else if (nums[i] == 2)
                swap(nums, i, --two);
            else{ // nums[i] == 0
                assert nums[i] == 0;
                swap(nums, ++zero, i++);
            }
        }
    }

    private void swap(int[] nums, int i, int j){
        int t = nums[i];
        nums[i]= nums[j];
        nums[j] = t;
    }

    public static void printArr(int[] nums){
        for(int num: nums)
            System.out.print(num + " ");
        System.out.println();
    }

    public static void main(String[] args) {

        int[] nums = {2, 2, 2, 1, 1, 0};
        (new Solution2()).sortColors(nums);
        printArr(nums);
    }
}