Next Day - Practice Coding Problems

Next Day - Problem

JavaScript Easy

Enhance JavaScript Date Objects with Next Day Functionality

Your task is to extend the JavaScript Date prototype by adding a custom nextDay() method that returns the next calendar day in ISO format.

Goal: Write code that allows any Date object to call date.nextDay() and receive the next day as a string in YYYY-MM-DD format.

Input: Any valid Date object
Output: String representing the next day in ISO format

Example:
const today = new Date('2023-12-31');
console.log(today.nextDay()); // "2024-01-01"

This problem tests your understanding of JavaScript prototypes, date manipulation, and handling edge cases like month boundaries, leap years, and year transitions.

Input & Output

example_1.js — Year Boundary

$ Input: const date = new Date('2023-12-31'); date.nextDay();

› Output: "2024-01-01"

💡 Note: December 31st rolls over to January 1st of the next year, demonstrating year boundary handling.

example_2.js — Month Boundary

$ Input: const date = new Date('2023-04-30'); date.nextDay();

› Output: "2023-05-01"

💡 Note: April 30th (last day of April) advances to May 1st, showing month boundary transition.

example_3.js — Leap Year

$ Input: const date = new Date('2024-02-28'); date.nextDay();

› Output: "2024-02-29"

💡 Note: In leap year 2024, February 28th advances to February 29th instead of March 1st.

Constraints

The method should be added to Date.prototype
Return format must be exactly YYYY-MM-DD
Must handle all edge cases: leap years, month boundaries, year transitions
Should not mutate the original Date object
Input dates are valid JavaScript Date objects

Visualization

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Understanding the Visualization

Copy the Calendar

Make a copy so we don't mess up the original date

Tell it 'Add One Day'

JavaScript's Date.setDate() is like having a smart assistant

Magic Happens

December 32nd? No problem! → January 1st automatically

Get Clean Format

toISOString() gives us perfect YYYY-MM-DD format

Key Takeaway

🎯 Key Insight: JavaScript's Date.setDate() automatically handles calendar arithmetic - when you set day 32 of December, it becomes day 1 of January next year!

Asked in

G Google 23 f Meta 18 a Amazon 15 ⊞ Microsoft 12

The optimal solution leverages JavaScript's built-in Date arithmetic by using setDate(getDate() + 1). JavaScript automatically handles all edge cases including month boundaries, leap years, and year transitions. The key insight is that setDate(32) on December 31st automatically becomes January 1st of the next year, eliminating the need for manual calendar calculations.

Common Approaches

Approach	Time	Space	Notes
✓ Built-in Date Arithmetic (Optimal)	O(1)	O(1)	Leverage JavaScript's built-in date handling for automatic overflow management

Built-in Date Arithmetic (Optimal) — Algorithm Steps

Create a new Date object from the current date
Use getDate() to get the current day
Use setDate() to set the day to current day + 1
JavaScript automatically handles overflow (e.g., day 32 becomes day 1 of next month)
Use toISOString() to get YYYY-MM-DDTHH:MM:SS.sssZ format
Extract the date part (first 10 characters) to get YYYY-MM-DD

Visualization

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Step-by-Step Walkthrough

Create Date Copy

new Date(this) creates a copy to avoid mutation

Get Current Day

getDate() returns 31 for December 31st

Add One Day

setDate(31 + 1) = setDate(32)

JavaScript Magic

Day 32 of December automatically becomes Day 1 of January next year

Format Output

toISOString().split('T')[0] gives YYYY-MM-DD

Code -

solution.c — C

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

char* nextDayOptimal(const char* dateStr) {
    static char result[11];
    struct tm date = {0};
    
    // Parse the date string
    sscanf(dateStr, "%d-%d-%d", &date.tm_year, &date.tm_mon, &date.tm_mday);
    date.tm_year -= 1900; // tm_year is years since 1900
    date.tm_mon -= 1;     // tm_mon is 0-11
    
    // Convert to time_t and add one day
    time_t time = mktime(&date);
    time += 24 * 60 * 60; // Add 24 hours
    
    // Convert back to struct tm
    struct tm* next_date = localtime(&time);
    
    // Format the result
    strftime(result, sizeof(result), "%Y-%m-%d", next_date);
    return result;
}

int main() {
    printf("%s\n", nextDayOptimal("2023-12-31"));
    return 0;
}

Time & Space Complexity

Time Complexity

⏱️

O(1)

Constant time operations using built-in Date methods

✓ Linear Growth

Space Complexity

O(1)

Only creating one temporary Date object

✓ Linear Space

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Smart Actions

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Input & Output

Constraints

Visualization

Related Problems

Common Approaches

Built-in Date Arithmetic (Optimal) — Algorithm Steps

Visualization

Code -

Time & Space Complexity

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