217. 存在重复元素

    public boolean containsDuplicate(int[] nums) {
        final int length = nums.length;
        Set<Integer> set = new HashSet<>();
        for (int i = 0; i < length; i++) {
            set.add(nums[i]);
            if (set.size() != (i + 1)) {
                return true;
            }
        }
        return false;
    }

    public boolean containsDuplicate2(int[] nums) {
        Set<Integer> set = new HashSet<>();
        for (int i : nums) {
            if (set.contains(i)) {
                return true;
            }
            set.add(i);
        }
        return false;
    }

    public boolean containsDuplicate3(int[] nums) {
        Arrays.sort(nums);
        for (int i = 0; i < nums.length - 1; i++) {
            if (nums[i] == nums[i + 1]) {
                return true;
            }
        }
        return false;
    }