class Solution {
    public void sortColors(int[] nums) {
        int left = 0, right = nums.length-1;
        int i = 0;
        while (i <= right) {
            if (nums[i] == 0) {
                swap(nums, i, left);
                i++;
                left++;
            } else if (nums[i] == 1) {
                i++;
            } else if (nums[i] == 2) {
                swap(nums, i, right);
                right--;
            }
        }
    }
    
    private void swap(int[] nums, int i, int j) {
        int tmp = nums[i];
        nums[i] = nums[j];
        nums[j] = tmp;
    }
}