Tags: #◇Computer Science #◇CSALGCM #◇Algorithms and Complexity #◇HackerRank #◇Fool Arcana #◇Implementation #◇Conditionals

Library Fine

◇Problem Description

A library charges fines for late book returns. Given the actual return date and the due date, calculate the fine.

Fine Rules:

Returned before or on the due date: No fine (0)
Returned after the due day (same month and year): 15 × (days late)
Returned after the due month (same year): 500 × (months late)
Returned after the due year: flat fine of 10,000

Input Format:

Line 1: d1 m1 y1 — actual return date
Line 2: d2 m2 y2 — due date

Output Format:

A single integer: the fine amount.

Sample:

Input	Output	Reason
`9 6 2015` `6 6 2015`	`45`	Same year, same month. 3 days late → 15 × 3 = 45
`1 1 2016` `1 1 2015`	`10000`	Different year, always flat 10000
`5 3 2015` `5 4 2015`	`0`	Returned before due date

◇Approach & Intuition

This is a cascading conditional (priority-ordered if-else) problem. The key is to check conditions in the right order — from coarsest granularity (year) down to finest (day):

Check year first: If y1 > y2, the penalty is always flat regardless of month/day.
Check month next (only if same year): If m1 > m2, charge per month.
Check day last (only if same year and month): If d1 > d2, charge per day.
Otherwise: Return 0 (on time or early).

[!warning] Common Mistake
Do NOT use a combined date comparison like return15 * (d1-d2) without first checking that y1 == y2 && m1 == m2. If the return is in a different month or year, the day difference is meaningless.

◇Complexity Analysis

	Complexity
Time	$O(1)$ — a fixed number of comparisons regardless of input size.
Space	$O(1)$ — six integer variables, no dynamic allocation.

◇Original Stub (HackerRank Template)

『』

CPP

#include <bits/stdc++.h>

using namespace std;

string ltrim(const string &);
string rtrim(const string &);
vector<string> split(const string &);

/*
 * Complete the 'libraryFine' function below.
 *
 * The function is expected to return an INTEGER.
 * The function accepts following parameters:
 *  1. INTEGER d1
 *  2. INTEGER m1
 *  3. INTEGER y1
 *  4. INTEGER d2
 *  5. INTEGER m2
 *  6. INTEGER y2
 */

int libraryFine(int d1, int m1, int y1, int d2, int m2, int y2) {

}

int main()
{
    ofstream fout(getenv("OUTPUT_PATH"));

    string first_multiple_input_temp;
    getline(cin, first_multiple_input_temp);

    vector<string> first_multiple_input = split(rtrim(first_multiple_input_temp));

    int d1 = stoi(first_multiple_input[0]);

    int m1 = stoi(first_multiple_input[1]);

    int y1 = stoi(first_multiple_input[2]);

    string second_multiple_input_temp;
    getline(cin, second_multiple_input_temp);

    vector<string> second_multiple_input = split(rtrim(second_multiple_input_temp));

    int d2 = stoi(second_multiple_input[0]);

    int m2 = stoi(second_multiple_input[1]);

    int y2 = stoi(second_multiple_input[2]);

    int result = libraryFine(d1, m1, y1, d2, m2, y2);

    fout << result << "\n";

    fout.close();

    return 0;
}

string ltrim(const string &str) {
    string s(str);

    s.erase(
        s.begin(),
        find_if(s.begin(), s.end(), not1(ptr_fun<int, int>(isspace)))
    );

    return s;
}

string rtrim(const string &str) {
    string s(str);

    s.erase(
        find_if(s.rbegin(), s.rend(), not1(ptr_fun<int, int>(isspace))).base(),
        s.end()
    );

    return s;
}

vector<string> split(const string &str) {
    vector<string> tokens;

    string::size_type start = 0;
    string::size_type end = 0;

    while ((end = str.find(" ", start)) != string::npos) {
        tokens.push_back(str.substr(start, end - start));

        start = end + 1;
    }

    tokens.push_back(str.substr(start));

    return tokens;
}

◇Full Solution

『』

CPP

#include <bits/stdc++.h>

using namespace std;

string ltrim(const string &);
string rtrim(const string &);
vector<string> split(const string &);

/*
 * Complete the 'libraryFine' function below.
 *
 * The function is expected to return an INTEGER.
 * The function accepts following parameters:
 *  1. INTEGER d1  (actual return day)
 *  2. INTEGER m1  (actual return month)
 *  3. INTEGER y1  (actual return year)
 *  4. INTEGER d2  (due day)
 *  5. INTEGER m2  (due month)
 *  6. INTEGER y2  (due year)
 */

int libraryFine(int d1, int m1, int y1, int d2, int m2, int y2) {
    // Returned after the due year
    if (y1 > y2) return 10000;
    // Returned in the same year but after the due month
    if (y1 == y2 && m1 > m2) return 500 * (m1 - m2);
    // Returned in the same year and month but after the due day
    if (y1 == y2 && m1 == m2 && d1 > d2) return 15 * (d1 - d2);
    // On time or early
    return 0;
}

int main()
{
    ofstream fout(getenv("OUTPUT_PATH"));

    string first_multiple_input_temp;
    getline(cin, first_multiple_input_temp);

    vector<string> first_multiple_input = split(rtrim(first_multiple_input_temp));

    int d1 = stoi(first_multiple_input[0]);

    int m1 = stoi(first_multiple_input[1]);

    int y1 = stoi(first_multiple_input[2]);

    string second_multiple_input_temp;
    getline(cin, second_multiple_input_temp);

    vector<string> second_multiple_input = split(rtrim(second_multiple_input_temp));

    int d2 = stoi(second_multiple_input[0]);

    int m2 = stoi(second_multiple_input[1]);

    int y2 = stoi(second_multiple_input[2]);

    int result = libraryFine(d1, m1, y1, d2, m2, y2);

    fout << result << "\n";

    fout.close();

    return 0;
}

string ltrim(const string &str) {
    string s(str);

    s.erase(
        s.begin(),
        find_if(s.begin(), s.end(), not1(ptr_fun<int, int>(isspace)))
    );

    return s;
}

string rtrim(const string &str) {
    string s(str);

    s.erase(
        find_if(s.rbegin(), s.rend(), not1(ptr_fun<int, int>(isspace))).base(),
        s.end()
    );

    return s;
}

vector<string> split(const string &str) {
    vector<string> tokens;

    string::size_type start = 0;
    string::size_type end = 0;

    while ((end = str.find(" ", start)) != string::npos) {
        tokens.push_back(str.substr(start, end - start));

        start = end + 1;
    }

    tokens.push_back(str.substr(start));

    return tokens;
}

Related Notes: ◇Computational Thinking in Problem Solving
Previous Problem: ◇04 - CamelCase
Next Problem: ◇06 - Minimum Distances
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05 - LIBRARY FINE