Given an integer array of size n, find all elements that appear more than ? n/3 ? times. 
The algorithm should run in linear time and in O(1) space.

 public List<Integer> majorityElement(int[] nums) {
       List<Integer> list = new ArrayList<>();
       if (nums == null || nums.length == 0) {
           return list;
       }
       if (nums.length == 1) {
           list.add(nums[0]);
           return list;
       }
       int ans1 = 0, ans2 = 0;
       int count1 = 0, count2 = 0;
       for (int i = 0; i < nums.length; i++) {
           if (nums[i] != ans1 && nums[i] != ans2) {
               if (count1 == 0) {
                   ans1 = nums[i];
                   count1++;
               } else if (count2 == 0) {
                   ans2 = nums[i];
                   count2++;
               } else {
                   count1--;
                   count2--;
               }
           } else if (nums[i] == ans1) {
               count1++;
           } else {
               count2++;
           }
       }
       count1 = 0;
       count2 = 0;
       
       for (int i : nums) {
           if (i == ans1) {
               count1++;
           } else if (i == ans2) {
               count2++;
           }
       }
       if (count1 > nums.length / 3) {
           list.add(ans1);
       }
       if (count2 > nums.length / 3) {
           list.add(ans2);
       }
       return list;
}