Next Day - Practice Coding Problems

Next Day - Problem

JavaScript Easy

Write code that enhances all Date objects such that you can call the date.nextDay() method on any date object and it will return the next day in the format YYYY-MM-DD as a string.

Your task is to modify the Date prototype to add a nextDay() method that correctly handles:

Regular day increments
Month boundaries (e.g., January 31 → February 1)
Year boundaries (e.g., December 31 → January 1 of next year)
Leap years (February 28/29 transitions)

The method should return a string in ISO date format (YYYY-MM-DD) representing the day immediately following the given date.

Input & Output

Example 1 — Regular Day Increment

$ Input: dateString = "2023-06-15"

› Output: "2023-06-16"

💡 Note: Simple case: June 15th becomes June 16th, no boundary crossing needed

Example 2 — Month Boundary

$ Input: dateString = "2023-01-31"

› Output: "2023-02-01"

💡 Note: End of January rolls over to beginning of February

Example 3 — Year Boundary

$ Input: dateString = "2023-12-31"

› Output: "2024-01-01"

💡 Note: New Year's Eve rolls over to New Year's Day of the next year

Constraints

Input date string is always in YYYY-MM-DD format
Year range: 1000 ≤ year ≤ 9999
Date represents a valid calendar date
Must handle leap years correctly

Visualization

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Understanding the Visualization

Input

Date string in YYYY-MM-DD format

Process

Add one day handling boundaries

Output

Next day in same format

Key Takeaway

🎯 Key Insight: Use built-in date libraries to automatically handle complex calendar arithmetic rather than manual edge case management

Asked in

G Google 25 a Amazon 20 M Microsoft 18 f Meta 15

The key insight is to leverage built-in date libraries rather than manually handling all edge cases. The optimal approach uses JavaScript's Date arithmetic with setDate(getDate() + 1) which automatically handles month boundaries, year rollovers, and leap years. Time: O(1), Space: O(1)

Common Approaches

Approach	Time	Space	Notes
✓ JavaScript Date Arithmetic	O(1)	O(1)	Use JavaScript's built-in Date object to handle date arithmetic automatically
Manual Date Calculation	O(1)	O(1)	Manually handle all date increment logic with conditional checks

JavaScript Date Arithmetic — Algorithm Steps

Create Date object from input string
Use setDate(getDate() + 1) to add one day
JavaScript automatically handles all overflow cases
Format result using toISOString() and extract date part

Visualization

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Step-by-Step Walkthrough

Create Date

new Date(dateString) parses input

Add Day

setDate(getDate() + 1) increments

Auto-Handle

JavaScript manages all overflows

Code -

solution.c — C

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

char* solution(char* dateString) {
    int year, month, day;
    sscanf(dateString, "%d-%d-%d", &year, &month, &day);
    
    // Create tm struct
    struct tm timeinfo = {0};
    timeinfo.tm_year = year - 1900;
    timeinfo.tm_mon = month - 1;
    timeinfo.tm_mday = day;
    
    // Convert to time_t and add one day
    time_t time = mktime(&timeinfo);
    time += 24 * 60 * 60; // Add 24 hours
    
    // Convert back to tm struct
    struct tm* nextTimeinfo = localtime(&time);
    
    // Format result
    char* result = malloc(11);
    sprintf(result, "%04d-%02d-%02d", 
            nextTimeinfo->tm_year + 1900, 
            nextTimeinfo->tm_mon + 1, 
            nextTimeinfo->tm_mday);
    return result;
}

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

Time & Space Complexity

Time Complexity

⏱️

O(1)

Built-in Date operations are constant time

✓ Linear Growth

Space Complexity

O(1)

Only creates one Date object

✓ Linear Space

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Input & Output

Constraints

Visualization

Related Problems

Common Approaches

JavaScript Date Arithmetic — Algorithm Steps

Visualization

Code -

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