80. Remove Duplicates from Sorted Array II

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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.

解法1：

还是双指针。用一个慢指针p来记录下一个需要插入的位置。一开始快慢指针都在一起。然后比较快指针p所对应的元素与p-2所对应的元素。
C++

1

Java

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public class Solution {
    public int removeDuplicates(int[] nums) {
        if (nums == null || nums.length == 0) {
            return 0;
        }
        if (nums.length <= 2) {
            return nums.length;
        }
        int p = 2, i = 2;
        while (i < nums.length) {
            if (nums[i] != nums[p - 2]) {
                nums[p++] = nums[i];
            }
            i++;
        }
        return p;
    }
}