448. 找到所有数组中消失的数字

    public List findDisappearedNumbers(int[] nums) {
        List list = new ArrayList<>();
        Set set = new HashSet<>();
        for (int num : nums) {
            set.add(num);
        }

        for (int i = 1; i <= nums.length; i++) {
            if ( !set.contains(i) ) list.add(i);
        }
        return list;
    }

    public static List findDisappearedNumbers1(int[] nums) {

        List list = new ArrayList<>();

        for (int i = 0; i < nums.length; i++) {
            int num = Math.abs(nums[i]);
            if (nums[num-1] > 0) {
                nums[num-1] = -nums[num-1];
            }
        }
        for (int i = 0; i < nums.length; i++) {
            int num = nums[i];
            if (num>0) list.add(i+1);
        }
        return list;
    }