Remove Duplicates from Sorted Array II

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.

题目大意：给定一个已经排好序的数组，去重，每个数字至多出现2次，返回去重后数组的长度，去重在原数组上进行。

题目难度：Medium

/**
 * Created by gzdaijie on 16/6/4
 * 使用isDup记录是否新加的数已经出现过
 * 空间复杂度O(1)，时间复杂度O(N)
 */
public class Solution {
    public int removeDuplicates(int[] nums) {
        if (nums.length < 3) return nums.length;

        int k = 0;
        int last = nums[0];
        boolean isDup = false;
        for (int i = 1; i < nums.length; i++) {
            if (nums[i] != last) {
                nums[++k] = last = nums[i];
                isDup = false;
                continue;
            }
            if (isDup) continue;
            nums[++k] = last;
            isDup = true;
        }
        return k + 1;
    }
}