#2880 Select Data - Solution

DataFrame students
+-------------+--------+
| Column Name | Type   |
+-------------+--------+
| student_id  | int    |
| name        | object |
| age         | int    |
+-------------+--------+

Write a solution to select the name and age of the student with student_id = 101.

The result format is in the following example.

Example 1:
Input:
+------------+---------+-----+
| student_id | name    | age |
+------------+---------+-----+
| 101        | Ulysses | 13  |
| 53         | William | 10  |
| 128        | Henry   | 6   |
| 3          | Henry   | 11  |
+------------+---------+-----+
Output:
+---------+-----+
| name    | age | 
+---------+-----+
| Ulysses | 13  |
+---------+-----+
Explanation:
Student Ulysses has student_id = 101, we select the name and age.

The key idea in #2880 Select Data is to retrieve only the required information from a dataset by applying the correct selection conditions. In most database-style problems, this is done using a SELECT statement combined with filtering conditions such as WHERE. Instead of processing every column or unnecessary rows, the goal is to extract just the fields that satisfy the given criteria.

Start by identifying which columns are needed in the output and which conditions determine whether a row should be included. Then construct a query that selects those columns while applying logical filters (such as equality checks or boolean conditions). This ensures the dataset is reduced efficiently and only the relevant records are returned.

Since the database typically scans rows to evaluate the conditions, the time complexity is proportional to the number of rows being checked. Proper indexing in real-world systems can further optimize this process, but the conceptual approach remains a straightforward filtering operation.

Approach	Time Complexity	Space Complexity
Filtering rows using SELECT with conditions	O(n)	O(1)

Solutions (10)

Approach 1: Iterate and Filter

Explanation: Iterator Filtering

This approach involves iterating through each record (or row) in the DataFrame and checking the 'student_id' against the specified value (101). Once a match is found, we can extract the 'name' and 'age' and return it as the result.

Time Complexity: O(n), where n is the number of students. We may have to check each student in the worst case.

Space Complexity: O(1), as no additional space beyond input storage is used.

C C++Java Python C#JavaScript

1#include <iostream>
2#include <vector>
3#include <string>
4
5struct Student {
6    int student_id;
7    std::string name;
8    int age;
9};
10
11void findStudent(const std::vector<Student>& students) {
12    for (const auto& student : students) {
13        if (student.student_id == 101) {
14            std::cout << "+---------+-----+\n";
            std::cout << "| " << student.name << " | " << student.age << " |\n";
            std::cout << "+---------+-----+\n";
            break;
        }
    }
}

int main() {
    std::vector<Student> students = {
        {101, "Ulysses", 13},
        {53, "William", 10},
        {128, "Henry", 6},
        {3, "Henry", 11}
    };
    findStudent(students);
    return 0;
}

Explanation

In C++, we use a struct to define the Student type, and a vector to hold all student records. The findStudent() function iterates through the vector to find the target student ID, then prints out the 'name' and 'age'.

Approach 2: HashMap/Dictionary Lookup

Explanation: Lookup with Map/Dictionary

This approach involves using a hash table, such as a Dictionary in Python or HashMap in Java, to store each student record with their student_id as the key. This enables direct access to a record based on student_id with average O(1) complexity, extracting 'name' and 'age' immediately.

Time Complexity: O(1), as hash table operations (get) average constant time.

Space Complexity: O(n), space usage increases with input size.

Java Python C#JavaScript

1using System;
2using System.Collections.Generic;

public class Student {
    public string Name { get; set; }
    public int Age { get; set; }
}

public class Program {
    public static void Main() {
        Dictionary<int, Student> studentsMap = new Dictionary<int, Student> {
            {101, new Student {Name = "Ulysses", Age = 13}},
            {53, new Student {Name = "William", Age = 10}},
            {128, new Student {Name = "Henry", Age = 6}},
            {3, new Student {Name = "Henry", Age = 11}}
        };

        if (studentsMap.TryGetValue(101, out Student student)) {
            Console.WriteLine("+---------+-----+");
            Console.WriteLine($"| {student.Name} | {student.Age} |");
            Console.WriteLine("+---------+-----+");
        }
    }
}