How do you solve Count Commas in Range on LeetCode?

Count Commas in Range (LeetCode #3870) 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: Numbers from 1000 to 9999 have exactly one comma.

What is the time complexity of Count Commas in Range?

The optimal solution for Count Commas in Range runs in O(1) time and uses O(1) space. Only a few arithmetic operations are performed, leading to constant time complexity.

What is the brute force solution for Count Commas in Range?

The brute force approach for Count Commas in Range is Brute Force, with O(n²) time complexity and O(1) space complexity. Count commas by converting each number to a string and checking its length. If it has 4 or more digits, count the commas. The optimal Optimal Solution approach improves this to O(1).

What algorithm or data structure is used to solve Count Commas in Range?

Count Commas in Range uses the following concepts: Math. The recommended patterns to study are: Mathematical counting, Range-based calculations.

What are the interview tips for Count Commas in Range?

Clarify the problem constraints and requirements. Think about edge cases, like n < 1000. Optimize your solution before coding.

What are common mistakes when solving Count Commas in Range?

Counting commas for numbers less than 1000. Miscalculating the range of numbers contributing commas.

#3870

Count Commas in Range

Easy

MathMathematical countingRange-based calculations

LeetCode ↗

Approaches

Brute ForceOptimal

Complexity Comparison

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

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Intuition

Time O(1)Space O(1)

Count commas directly based on the number of digits in the range. Numbers from 1000 to n will each contribute one comma.

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Algorithm

3 steps

1Step 1: If n < 1000, return 0.
2Step 2: Calculate the number of integers from 1000 to n, which is n - 999.
3Step 3: Return the count of integers from 1000 to n as the total number of commas.

solution.py2 lines

1def count_commas(n):
2    return max(0, n - 999)

ℹ

Complexity note: Only a few arithmetic operations are performed, leading to constant time complexity.

1Numbers from 1000 to 9999 have exactly one comma.
2Count commas based on ranges rather than individual numbers.

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