Remove Duplicates from Sorted Array II

Follow up for "Remove Duplicates":
What if duplicates are allowed at most twice?

For example,
Given sorted array A = [1,1,1,2,2,3],

Your function should return length = 5, and A is now [1,1,2,2,3].

Notes: this problem requires in-place array manipulation.
Solution1: run time complexity O(n), space complexity is constant space.

public class Solution {
    //no need to change the given array's size, 
    //only change the first k elements of the array which has duplicates removed.
    public int removeDuplicates(int[] A) {
        if(A == null || A.length == 0)
            return 0;
        
        boolean isSameTwo = false;
        int pre = A[0];
        int count = 0;
        
        int o = 1;
        
        for(int i = 1; i < A.length; i++) {
            int cur = A[i];
            
            if(cur == pre) {
                if(!isSameTwo) {
                    isSameTwo = true;
                    A[o] = cur;
                    o++;
                    continue;
                }else {
                    count++;
                }
            }else {
                pre = cur;
                A[o] = cur;
                o++;
                isSameTwo = false;
            }
        }
        return A.length - count;
    }
}

Solution2: run time complexity O(n), space complexity is constant space.

public class Solution {
    //no need to change the given array's size, 
    //only change the first k elements of the array which has duplicates removed.
    public int removeDuplicates(int[] A) {
        if(A.length < 2)
            return A.length;
        
        int pre = 1;
        int cur = 2;
        
        while(cur < A.length) {
            if(A[cur] == A[pre] && A[cur] == A[pre - 1]) {
                cur++;
            }else {
                pre++;
                A[pre] = A[cur];
                cur++;
            }
        }
        return pre + 1;
    }
}

Solution3:run time complexity O(n), space complexity is constant space.

public class Solution {
    public int removeDuplicates(int[] nums) {
        if (nums == null || nums.length == 0) {
            return 0;
        }
        
        int count = 1;
        boolean hasTwo = false;
        for (int i = 1; i < nums.length; i++) {
            if (nums[i] == nums[i - 1]) {
                if (!hasTwo) {
                    nums[count] = nums[i];
                    count++;
                    hasTwo = true;
                } else {
                    continue;
                }
            } else {
                nums[count] = nums[i];
                count++;
                hasTwo = false;
            }
        }
        
        return count;
    }
}