Maps-STL – HackerRank Solution

Maps-STL – HackerRank Solution

Problem :

Maps are a part of the C++ STL.Maps are associative containers that store elements formed by a combination of a key value and a mapped value, following a specific order.The mainly used member functions of maps are:

Map Template :

std::map <key_type, data_type>

Declaration :

map<string,int>m; //Creates a map m where key_type is of type string and data_type is of type int.

Size :

int length=m.size(); //Gives the size of the map.

Insert :

m.insert(make_pair("hello",9)); //Here the pair is inserted into the map where the key is "hello" and the value associated with it is 9.

Erasing an element :

m.erase(val); //Erases the pair from the map where the key_type is val.

Finding an element :

map<string,int>::iterator itr=m.find(val); //Gives the iterator to the element val if it is found otherwise returns m.end() .
Ex: map<string,int>::iterator itr=m.find("Maps"); //If Maps is not present as the key value then itr==m.end().

Accessing the value stored in the key :

To get the value stored of the key "MAPS" we can do m["MAPS"] or we can get the iterator using the find function and then by itr->second we can access the value.

To know more about maps click Here.

You are appointed as the assistant to a teacher in a school and she is correcting the answer sheets of the students.Each student can have multiple answer sheets.So the teacher has Q queries:

  1. X Y  :Add the marks Y to the student whose name is X.
  2. X : Erase the marks of the students whose name is X.
  3. X : Print the marks of the students whose name is X. (If X didn’t get any marks print 0.)

Sample Input :

7
1 Jesse 20
1 Jess 12
1 Jess 18
3 Jess
3 Jesse
2 Jess
3 Jess

Sample Output :

30
20
0

Solution :

#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <set>
#include <map>
#include <algorithm>
using namespace std;


int main() {
    int n, a, b;
    string name;
    cin >> n;
    map<string, int>m;
    for(int i = 0; i < n; i++) {
        cin >> a >> name;
        if(a == 1) {
            cin >> b;
            m[name] += b;
        } else if (a == 2) {
            m.erase(name);
        } else if (a == 3) {
            map<string, int>::iterator itr = m.find(name);
            cout << (itr == m.end() ? 0 : itr->second) << endl;
        }
    }
    return 0;
}

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