2.1.1Remove Duplicates from Sorted Array

description:
    Given a sorted array,remove the duplicates in place such that each element appear only once and return the new length;
    Do not allocate extra space for another array,you must do this in place with constant memory.
    For example,Given input array A = [1,1,2],
    Your function should return length = 2, and A is now [1,2]



code1:
//time : O(n), space:O(1)
class Solution{
    public:
        int removeDuplicates(vector<int>& nums){
            if(nums.empty()) return 0;
            int index = 0;
            for(int i = 1; i < nums.size(); i++){
                if(nums[index] != nums[i])
                    nums[++index] = nums[i];
            }
            return index + 1;
        }
};

code2:
class Solution{
    public:
        int removeDuplicates(vector<int>& nums){
            return distance(nums.begin(),unique(nums.begin(),nums.end()));
        }
}


code3:
class Solution{
    public:
        return distance(nums.begin(),removeDuplicates(nums.begin(),nums.end(),nums.begin()));
}

template<typename InIt, typename OutIt>
OutIt removeDuplicates(InIt first, InIt last, OutIt output){
    while(first != last){
        *output++ = *first;
        first = upper_bound(first,last,*first);
    }
    return Output;
}