Voting Eligibility - Problem

Given a person's birth date as a string in the format YYYY-MM-DD, determine if they are eligible to vote. A person is eligible to vote if they are 18 years or older.

If the person is eligible, return "Eligible". If they are not eligible, return the number of days until they become eligible as a string (e.g., "120").

Assume the current date is 2024-01-01 for all calculations.

Input & Output

Example 1 — Not Eligible Yet

$ Input: birthDate = "2010-06-15"

› Output: "1627"

💡 Note: Person born on 2010-06-15 will turn 18 on 2028-06-15. From current date 2024-01-01 to 2028-06-15 is 1627 days.

Example 2 — Just Became Eligible

$ Input: birthDate = "2006-01-01"

› Output: "Eligible"

💡 Note: Person born on 2006-01-01 turned 18 on 2024-01-01, which is exactly the current date. They are eligible to vote.

Example 3 — Long Time Eligible

$ Input: birthDate = "1990-03-20"

› Output: "Eligible"

💡 Note: Person born on 1990-03-20 turned 18 on 2008-03-20, which is long before current date 2024-01-01. They are eligible.

Constraints

Birth date is in valid YYYY-MM-DD format
Birth date is not in the future (before 2024-01-01)
1900 ≤ birth year ≤ 2023

Visualization

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Asked in

M Microsoft 15 a Amazon 12 G Google 8

The key insight is to calculate the person's 18th birthday by adding 18 years to their birth date, then directly compare it with the current date (2024-01-01). If the current date is on or after the 18th birthday, they are eligible. Otherwise, calculate the days between current date and 18th birthday. Best approach uses built-in date arithmetic for accurate calculations. Time: O(1), Space: O(1)

Common Approaches

✓ Day-by-Day Calculation

⏱️ Time: O(1) Space: O(1)

Parse the birth date and current date, then count the total number of days between them. Convert days to years to check if 18+ years have passed.

Direct Date Comparison

⏱️ Time: O(1) Space: O(1)

Parse birth date, add 18 years to get eligibility date, then directly compare with current date. Use built-in date arithmetic for precise calculations.

Day-by-Day Calculation — Algorithm Steps

Parse birth date and current date
Count total days between dates
Convert days to years (accounting for leap years)
Check if 18+ years have passed

Visualization

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Step-by-Step Walkthrough

Parse Dates

Convert birth date string and current date to date objects

Calculate Difference

Find days between current date and 18th birthday

Check Eligibility

If 18th birthday has passed, return 'Eligible', otherwise return days remaining

Code -

solution.c — C

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

char* solution(char* birthDate) {
    int birthYear, birthMonth, birthDay;
    sscanf(birthDate, "%d-%d-%d", &birthYear, &birthMonth, &birthDay);
    
    int currentYear = 2024, currentMonth = 1, currentDay = 1;
    int eighteenthYear = birthYear + 18;
    
    // Check if already eligible
    if (currentYear > eighteenthYear || 
        (currentYear == eighteenthYear && currentMonth > birthMonth) ||
        (currentYear == eighteenthYear && currentMonth == birthMonth && currentDay >= birthDay)) {
        char* result = malloc(10);
        strcpy(result, "Eligible");
        return result;
    }
    
    // Calculate days until eligibility (simplified)
    struct tm current = {0};
    current.tm_year = currentYear - 1900;
    current.tm_mon = currentMonth - 1;
    current.tm_mday = currentDay;
    
    struct tm eighteenth = {0};
    eighteenth.tm_year = eighteenthYear - 1900;
    eighteenth.tm_mon = birthMonth - 1;
    eighteenth.tm_mday = birthDay;
    
    time_t currentTime = mktime(&current);
    time_t eighteenthTime = mktime(&eighteenth);
    
    int daysUntil = (int)((eighteenthTime - currentTime) / (60 * 60 * 24));
    
    char* result = malloc(10);
    sprintf(result, "%d", daysUntil);
    return result;
}

int main() {
    char birthDate[20];
    fgets(birthDate, sizeof(birthDate), stdin);
    birthDate[strcspn(birthDate, "\n")] = 0;
    
    char* result = solution(birthDate);
    printf("%s\n", result);
    free(result);
    return 0;
}

Time & Space Complexity

Time Complexity

⏱️

O(1)

Fixed number of date calculations regardless of input

✓ Linear Growth

Space Complexity

O(1)

Only stores a few date variables and counters

✓ Linear Space

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Voting Eligibility - Problem

Input & Output

Constraints

Visualization

Related Problems

Common Approaches

Day-by-Day Calculation — Algorithm Steps

Visualization

Code -

Time & Space Complexity

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