Student Record Manager - Problem

You are tasked with building a Student Record Management System that can store and manage student information efficiently.

Each student record contains:

Name (string): Student's full name
ID (integer): Unique student identifier
Grades (array of integers): List of grades for different subjects

Your system should support the following operations:

Add Student: Add a new student record to the system
Search by ID: Find a student's complete record using their ID
Calculate Average Grade: Compute the average of all grades for a specific student

For this problem, implement a function that takes a list of student records and a target student ID, then returns that student's average grade. If the student is not found, return -1.0.

Input & Output

Example 1 — Basic Student Record

$ Input: students = [["Alice",101,[85,90,78]], ["Bob",102,[92,88,95]]], targetId = 102

› Output: 91.67

💡 Note: Student with ID 102 is Bob with grades [92,88,95]. Average = (92+88+95)/3 = 275/3 = 91.67

Example 2 — Student Not Found

$ Input: students = [["Alice",101,[85,90,78]], ["Bob",102,[92,88,95]]], targetId = 999

› Output: -1.0

💡 Note: No student has ID 999, so return -1.0 to indicate student not found

Example 3 — Single Grade

$ Input: students = [["Charlie",103,[95]]], targetId = 103

› Output: 95.0

💡 Note: Student 103 has only one grade [95], so average is 95.0

Constraints

1 ≤ students.length ≤ 1000
1 ≤ student ID ≤ 10⁶
1 ≤ grades.length ≤ 10
0 ≤ grade ≤ 100

Visualization

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Asked in

a Amazon 35 M Microsoft 28 G Google 22 🍎 Apple 18

The key insight is to search and calculate in a single pass rather than separate operations. When the target student ID is found, immediately calculate the average of their grades instead of doing a second loop. Best approach uses single-pass optimization with Time: O(n), Space: O(1).

Common Approaches

✓ Linear Search with Separate Average Calculation

⏱️ Time: O(n + g) Space: O(1)

First loop through all students to find the target ID. Once found, loop through all grades to calculate the sum and divide by count for average.

Single-Pass Search and Calculate

⏱️ Time: O(n) Space: O(1)

Iterate through students once. When target ID is found, immediately calculate the average of grades in the same loop iteration, then return the result.

Linear Search with Separate Average Calculation — Algorithm Steps

Iterate through each student record
Check if current student's ID matches target ID
If found, iterate through all grades to calculate sum
Divide sum by number of grades to get average

Visualization

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Step-by-Step Walkthrough

Start Search

Begin checking from first student record

Check IDs

Compare each student's ID with target ID

Calculate Average

When found, sum all grades and divide by count

Code -

solution.c — C

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

double solution(int students[][10], int studentCount, int* gradeCounts, int targetId) {
    // Find the student with matching ID
    int foundIndex = -1;
    for (int i = 0; i < studentCount; i++) {
        if (students[i][0] == targetId) {  // students[i][0] is ID
            foundIndex = i;
            break;
        }
    }
    
    if (foundIndex == -1) {
        return -1.0;
    }
    
    // Calculate average of grades (skip first element which is ID)
    int gradeCount = gradeCounts[foundIndex] - 1;
    if (gradeCount <= 0) {
        return 0.0;
    }
    
    int total = 0;
    for (int i = 1; i <= gradeCount; i++) {
        total += students[foundIndex][i];
    }
    
    return (double) total / gradeCount;
}

int main() {
    int students[100][10];  // Max 100 students, 10 values each (ID + grades)
    int gradeCounts[100];
    int studentCount = 0;
    int targetId;
    
    // Simple input parsing - in practice would need proper JSON parsing
    scanf("%d", &targetId);
    
    double result = solution(students, studentCount, gradeCounts, targetId);
    printf("%f\n", result);
    
    return 0;
}

Time & Space Complexity

Time Complexity

⏱️

O(n + g)

O(n) to find student + O(g) to calculate average where g is number of grades

✓ Linear Growth

Space Complexity

O(1)

Only using a few variables to store sum and count

✓ Linear Space

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Student Record Manager - Problem

Input & Output

Constraints

Visualization

Related Problems

Common Approaches

Linear Search with Separate Average Calculation — Algorithm Steps

Visualization

Code -

Time & Space Complexity

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