How do you solve Number of Days Between Two Dates on LeetCode?

Number of Days Between Two Dates (LeetCode #1360) can be solved using Brute Force or Optimal Solution. The optimal approach is Optimal Solution with O(1) time complexity and O(1) space complexity. Key insight: Understanding how to manipulate date formats is crucial for solving date-related problems.

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

The optimal solution for Number of Days Between Two Dates runs in O(1) time and uses O(1) space. This is constant time complexity since we are performing a fixed number of operations regardless of the input size.

What is the brute force solution for Number of Days Between Two Dates?

The brute force approach for Number of Days Between Two Dates is Brute Force, with O(n²) time complexity and O(1) space complexity. The brute force approach involves iterating through each day between the two dates and counting them. This is straightforward but inefficient for large date ranges. The optimal Optimal Solution approach improves this to O(1).

What algorithm or data structure is used to solve Number of Days Between Two Dates?

Number of Days Between Two Dates uses the following concepts: Math, String. The recommended patterns to study are: Date Manipulation, Mathematical Calculations.

What are the interview tips for Number of Days Between Two Dates?

Always clarify the input format and constraints before diving into the solution. Consider edge cases, such as dates that are the same or span multiple years. Explain your thought process clearly; interviewers appreciate understanding your reasoning.

What are common mistakes when solving Number of Days Between Two Dates?

Not accounting for leap years when calculating days. Confusing the order of dates and not taking the absolute difference.

#1360

Number of Days Between Two Dates

Easy

MathStringDate ManipulationMathematical Calculations

LeetCode ↗

Approaches

Brute ForceOptimal

Complexity Comparison

	Brute Force	Optimal Solution★
Time	O(n²)	O(1)
Space	O(1)	O(1)

💡

Intuition

Time O(1)Space O(1)

Instead of counting each day, we can calculate the total number of days from a fixed date (like 1900-01-01) to each date and then find the difference. This is much faster.

⚙️

Algorithm

3 steps

1Step 1: Create a function that calculates the number of days from a fixed date (e.g., 1900-01-01) to the given date.
2Step 2: Use this function to get the total days for both dates.
3Step 3: Return the absolute difference between the two day counts.

solution.py8 lines

1# Full working Python code
2from datetime import datetime
3
4def daysBetweenDates(date1: str, date2: str) -> int:
5    def countDays(date: str) -> int:
6        d = datetime.strptime(date, '%Y-%m-%d')
7        return (d - datetime(1900, 1, 1)).days
8    return abs(countDays(date1) - countDays(date2))

ℹ

Complexity note: This is constant time complexity since we are performing a fixed number of operations regardless of the input size.

1Understanding how to manipulate date formats is crucial for solving date-related problems.
2Using a fixed reference date simplifies calculations significantly.

Solutions and explanations are original Tejav content. Problem titles © LeetCode — use the LeetCode button above for the full problem statement.