class Solution {public:    int removeDuplicates(vector
    
     & nums) {        if (nums.empty()) return 0;        int pre = 0, cur = 0, n = nums.size();        while (cur < n) {            if (nums[pre] == nums[cur]) ++cur;            else nums[++pre] = nums[cur++];        }        return pre + 1;    }};