Is Number of Days Between Two Dates easy or hard?

LeetCode classifies this problem as Easy. The main challenge is correctly handling leap years and month lengths if implementing the manual calculation approach.

Number of Days Between Two Dates Python/Java solution

In Python, parse the strings using datetime.strptime and subtract the resulting date objects to obtain a timedelta, then return abs(delta.days). In Java, use LocalDate.parse and ChronoUnit.DAYS.between to compute the difference. Both implementations run in O(1) time.

How to solve Number of Days Between Two Dates in O(1)?

Convert both dates into a total day count from a fixed reference date. Add days from previous years (including leap years), add days from previous months in the current year, then add the day value. Compute the absolute difference between the two totals. Since the number of months and calculations is constant, the complexity is O(1).

What is the best approach for Number of Days Between Two Dates?

The most practical approach uses built-in date libraries such as Python's datetime, Java's LocalDate, or JavaScript's Date. Parse both YYYY-MM-DD strings into date objects and subtract them to get the day difference. This runs in O(1) time and avoids manual leap-year and month calculations.

Is Number of Days Between Two Dates asked at Google/Amazon/Meta?

Date arithmetic and calendar calculation problems appear in interviews at companies like Google and Amazon because they test edge-case handling and logical reasoning. Variations include computing day differences, validating dates, or implementing calendar utilities.

What data structure is used in Number of Days Between Two Dates?

The solution mainly relies on arrays and simple arithmetic. An array storing the number of days in each month helps when performing manual calculations, while string parsing extracts the year, month, and day values from the input.

What is the time complexity of Number of Days Between Two Dates?

Both common approaches run in O(1) time because the input format is fixed-length and the operations involve constant-size calculations. Parsing the date string and computing the difference between two date values does not depend on input size. Space complexity is also O(1).

Description Hints 4 Solution Video 3:03

1360. Number of Days Between Two Dates

Easy53.7% acceptance4 companies

Write a program to count the number of days between two dates.

The two dates are given as strings, their format is YYYY-MM-DD as shown in the examples.

Example 1:

Input: date1 = "2019-06-29", date2 = "2019-06-30"
Output: 1

Example 2:

Input: date1 = "2020-01-15", date2 = "2019-12-31"
Output: 15

Constraints:

The given dates are valid dates between the years 1971 and 2100.

Asked at 4 companies

Optiver

Google Amazon Meta

Topics

Math String

Hints open one at a time

Hint 1

Create a function f(date) that counts the number of days from 1900-01-01 to date. How can we calculate the answer ?

Hint 2

The answer is just |f(date1) - f(date2)|.

Hint 3

How to construct f(date) ?

Hint 4

For each year from 1900 to year - 1 sum up 365 or 366 in case of leap years. Then sum up for each month the number of days, consider the case when the current year is leap, finally sum up the days.

3:03

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