594. Longest Harmonious Subsequence

class Solution {
public:
    int findLHS(vector<int>& nums) {
        if(nums.empty())
            return 0;
        map<int,int> map1;
        for(int i=0;i<nums.size();i++){
            map1[nums[i]]++;
        }
        map<int,int>::iterator iter1=map1.begin();
        map<int,int>::iterator iter2=map1.begin();
        iter2++;
        int res=0;
        for(;iter2!=map1.end();iter1++,iter2++){
            if(iter2->first-iter1->first == 1){
                int temp=iter1->second+iter2->second;
                res=res>temp ? res :temp;
            }
        }
        return res;
    }
};