Remove Duplicates from Sorted Array II

Problem

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

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

Your function should return length = 5, with the first five elements of nums being 1, 1, 2, 2 and 3. It doesn't matter what you leave beyond the new length.

Solution

Verbose Solution

public class Solution {
    public int removeDuplicates(int[] nums) {
        if (nums == null || nums.length == 0) return 0;
        int index = 0, count = 0, cur = nums[0];
        for (int num : nums) {
            if (num == cur) count++;
            else {
                count = 1;
                cur = num;
            }
            if (count < 3) nums[index++] = num;  
        }
        return index;
    }
}

Concise Solution

public class Solution {
    public int removeDuplicates(int[] nums) {
        int index = 0;
        for (int num : nums) {
            if (index < 2 || num != nums[index - 2]) nums[index++] = num;
        }
        return index;
    }
}

Analysis

The first problem uses count and cur to check duplicates
The second solution uses formula num == nums[index - x] where x represents the times of duplicates allow