class Solution {
public:
    int removeDuplicates(vector<int>& 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;
    }
};