677. Map Sum Pairs

类的操作，之前写过比较长的C++代码之后，基本用法都知道了。注意：可以定义私有变量哦！

class MapSum {private:    map<string, int> pairs;public:    /** Initialize your data structure here. */    MapSum() {    }    void insert(string key, int val) {        if(pairs.find(key)==pairs.end())            pairs[key] =val;        else            pairs[key]=val;    }    int sum(string prefix) {        int result=0;        for(map<string, int>::iterator it= pairs.begin();it!=pairs.end();it++)        {            string a = it->first;            int b = it->second;            // search perfix from a            if(a.substr(0,prefix.size())==prefix)                result+=b;        }        return result;    }};/** * Your MapSum object will be instantiated and called as such: * MapSum obj = new MapSum(); * obj.insert(key,val); * int param_2 = obj.sum(prefix); */