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;    }};