Multi-set for user defined data type

You are given Q queries. Each query contains an integer k and a person’s information i.e, first name, last name, age. For each query, we need to output Kth person among them if all person information are arrange in ascending order.
Note: Person A comes before person B if first name of A is lexicographic smaller than that of B. But if first name is same then we compare last name and also if last name also same then we have to compare their ages.

Given: K will always less than or equal to number of person present.
Examples:

Input : Q = 2
        1
        aa bb 10
        2 
        bb cc 10
Output :
First name:aa
Last name:bb
Age: 10

First name:bb
Last name:cc
Age: 10

Approach: The below algorithm is followed to solve the above problem.

• Basically we are given a person detail with each query and we have to tell Kth person if they are arranged in ascending order.
• Basic approach: After each query, we sort our list and just print kth person’s detail. But if we solve the above problem using sorting then time complexity will be O(q*q*log(q)). i.e, O(qlog(q)) for sorting each time and q queries.
• Optimized : We can improve time complexity for the problem stated above.As we know insertion in multiset can be done in log(n).
• So, just make a multiset which can be use for storing structure, and then After each query just insert the person’s detail in our multiset.
• So, this seems to be better approach.Our overall complexity will be O(q*log(q)).

// CPP program for queries to find k-th person where
// people are considered in lexicographic order of
// first name, then last name, then age
#include <bits/stdc++.h>
using namespace std;

struct person {
    string firstName, lastName;
    int age;
};

// operator overloading to use multiset for user
// define data type.
bool operator<(person a, person b)
{
    if (a.firstName < b.firstName)
        return true;
    else if (a.firstName == b.firstName) {
        if (a.lastName < b.lastName)
            return true;
        else if (a.lastName == b.lastName) {
            if (a.age < b.age)
                return true;
            else
                return false;
        }
        else
            return false;
    }
    else
        return false;
}

// define function for printing our output
void print(multiset<person>::iterator it)
{
    cout << "First name:" << it->firstName << endl;
    cout << "Last name:" << it->lastName << endl;
    cout << "Age: " << it->age << endl;
}

int main()
{
    int q = 2;

    // define set for structure
    multiset<person> s;

    // declaration of person structure
    person p;

    // 1st Query k=1, first-name=aa, last-name=bb, age=10;
    int k = 1;
    p.firstName = "aa";
    p.lastName = "bb";
    p.age = 10;

    // now insert this structure in our set.
    s.insert(p);

    // now find Kth smallest element in set.
    multiset<person>::iterator it;
    it = s.begin();

    // find kth element by increment iterator by k
    std::advance(it, k - 1);
    print(it);

    // 2nd Query k=2, first-name=bb, last-name=cc, age=10;
    k = 2;
    p.firstName = "bb";
    p.lastName = "cc";
    p.age = 10;

    // now insert this structure in our set.
    s.insert(p);

    // now find Kth smallest element in set.
    it = s.begin();

    // find kth element by increment iterator by k
    std::advance(it, k - 1);
    print(it);
    return 0;
}

Output:

First name:aa
Last name:bb
Age: 10
First name:bb
Last name:cc
Age: 10