leetcode 80: Remove Duplicates from Sorted Array II

class Solution {
public:
    int removeDuplicates(vector<int>& nums) {
        map<int,int> mp;
        int len=nums.size();
        for(int i=0;i<len;i++)
        {
            if(mp.find(nums[i])==mp.end())
                mp[nums[i]]=1;
            else if(mp[nums[i]]==1)
                mp[nums[i]]++;
            else if(mp[nums[i]]==2)
            {
                for(int j=i+1;j<len;j++)
                    nums[j-1]=nums[j];
                len--;
                i--;
            }
        }
        return len;
    }
};