leetcode 26: Remove Duplicates from Sorted Array

class Solution {
public:
int removeDuplicates(vector<int>& nums) {
if(nums.empty())
return 0;
int res=1;
int old=0;
for(int i=1;i<nums.size();i++)
if(nums[i]!=nums[i-1])
{
res++;
if(i-old==1)
old++;
else
{
nums[old+1]=nums[i];
old++;
}
}
return res;
}
};