sort colors

public void (int[] nums) {
    int[] colors = new int[3];
    for (int i : nums) {
        colors[i]++;
    }
    int index = 0;
    int color = 0;
    for (int i : colors) {
        while (i-- > 0) {
            nums[index++] = color;
        }
        ++color;
    }
}

public void (int[] nums) {
    if (nums == null || nums.length == 0)
        return;
    int left = 0, right = nums.length - 1;
    for (int i = 0; i <= right;) {
        if (nums[i] == 2) {
            swap(nums, i, right);
            --right;
        } else if (nums[i] == 0) {
            swap(nums, i, left);
            ++left;
            ++i;
        } else
            ++i;
    }
}

public void swap(int[] nums, int i, int j) {
    int temp = nums[i];
    nums[i] = nums[j];
    nums[j] = temp;
}