677. Map Sum Pairs

Implement a MapSum class with insert, and sum methods.

For the method insert, you'll be given a pair of (string, integer). The string represents the key and the integer represents the value. If the key already existed, then the original key-value pair will be overridden to the new one.

For the method sum, you'll be given a string representing the prefix, and you need to return the sum of all the pairs' value whose key starts with the prefix.

Example 1:

Input: insert("apple", 3), Output: Null
Input: sum("ap"), Output: 3
Input: insert("app", 2), Output: Null
Input: sum("ap"), Output: 5

class MapSum {
    map<string, int> mp;
public:
    /** Initialize your data structure here. */
    MapSum() {}
    
    void insert(string key, int val) {
        mp[key]=val;
    }
    
    int sum(string prefix) {
        /*
        if (mp.find(prefix)==mp.end()){
            return 0;
        }
        */
        int res=0, n=prefix.size();
        
        for(auto iter=mp.lower_bound(prefix);iter!=mp.end();++iter)
        {
            if(iter->first.substr(0,n)!=prefix)
                break;
            res+=iter->second;
        }
        return res;
    }
};

/**
 * Your MapSum object will be instantiated and called as such:
 * MapSum obj = new MapSum();
 * obj.insert(key,val);
 * int param_2 = obj.sum(prefix);
 */

c++ map lower_bound upper_bound用法

运行 https://www.cnblogs.com/billin/archive/2011/09/01/2162102.html 一下代码就知道了

#include<map>
#include<iostream>
int main()
{
    using namespace std;
    map<int,int> m1;
    map<int,int>::const_iterator m1_AcIter,m1_RcIter;
    typedef pair<int,int> Int_Pair;
    m1.insert(Int_Pair(1,10));
    m1.insert(Int_Pair(2,20));
    m1.insert(Int_Pair(3,30));
    m1_RcIter=m1.lower_bound(2);
    cout<<"The first elem of map m1 with a key greater than 2 is: "
    <<m1_RcIter->second<<"."<<endl;
    m1_RcIter=m1.lower_bound(4);
    if(m1_RcIter==m1.end())
    {
        cout<<"The map m1 doesn't have an element with a key of 4."<<endl;
    }
    else
    {
        cout<<"The element of map m1 with a key of 4 is: "<<m1_RcIter->second<<"."<<endl;
    }
    
    m1_AcIter=m1.end();
    m1_AcIter--;
    m1_RcIter=m1.lower_bound(m1_AcIter->first);
    cout<<"The element of m1 with a key mathing the last element is: "
    <<m1_RcIter->second<<"."<<endl;
    return 1;
    
}

输出

python代码

class MapSum(object):

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.d={}
        

    def insert(self, key, val):
        """
        :type key: str
        :type val: int
        :rtype: void
        """
        self.d[key]=val
        

    def sum(self, prefix):
        """
        :type prefix: str
        :rtype: int
        """
        return sum(self.d[i] for i in self.d if i.startswith(prefix)) 
        


# Your MapSum object will be instantiated and called as such:
# obj = MapSum()
# obj.insert(key,val)
# param_2 = obj.sum(prefix)