题目：

题解：

class Solution {
public:
    int removeDuplicates(vector<int>& nums) {
        int n = nums.size();
        if (n <= 2) {
            return n;
        }
        int slow = 2, fast = 2;
        while (fast < n) {
            if (nums[slow - 2] != nums[fast]) {
                nums[slow] = nums[fast];
                ++slow;
            }
            ++fast;
        }
        return slow;
    }
};