3870 LeetCode problem solution

Another LeetCode problem that can be solved with just one line of code. No number can contain more than one comma. Numbers from 1 to 999 contain 0 commas, while every number from 1000 to n contains exactly 1.

So the total number of commas is simply the number of integers in the range [1000, n]:

n - 1000 + 1 = n - 999

This solution is optimal specifically because of the constraint n <= 10⁵.

Time complexity: O(1)
Space complexity: O(1)

If you want to see how the same problem can require a different solution when the constraints change, compare LeetCode 3870 and 3871 in this post.

LeetCode 3870 C++ solution

class Solution {
public:
  int countCommas(int n) 
  {
    return max(0, n - 999);
  }
};

LeetCode 3870 Java solution

class Solution {
  public int countCommas(int n) {
    return Math.max(0, n - 999);
  }
}

LeetCode 3870 JavaScript solution

var countCommas = function(n) {
  return Math.max(0, n - 999);
};

LeetCode 3870 TypeScript solution

function countCommas(n: number): number {
  return Math.max(0, n - 999);
};

LeetCode 3870 Python solution

class Solution(object):
  def countCommas(self, n):
    return max(0, n - 999)