LC-2180 Easy LeetCode

2180. Count Integers With Even Digit Sum

Read the full problem statement on LeetCode.

Difficulty: easy Acceptance: 69% Topics: Math, Simulation

Reading material

Math & Geometry 12 min Simulation & Enumeration 9 min

Reference solution (spoiler · python)

# Time:  O(logn)
# Space: O(1)

# math
class Solution(object):
    def countEven(self, num):
        """
        :type num: int
        :rtype: int
        """
        def parity(x):
            result = 0
            while x:
                result += x%10
                x //= 10
            return result%2

        return (num-parity(num))//2


# Time:  O(nlogn)
# Space: O(1)
# brute force
class Solution2(object):
    def countEven(self, num):
        """
        :type num: int
        :rtype: int
        """
        def parity(x):
            result = 0
            while x:
                result += x%10
                x //= 10
            return result%2

        return sum(parity(x) == 0 for x in xrange(1, num+1))


# Time:  O(nlogn)
# Space: O(logn)
# brute force
class Solution3(object):
    def countEven(self, num):
        """
        :type num: int
        :rtype: int
        """
        return sum(sum(map(int, str(x)))%2 == 0 for x in xrange(1, num+1))

Solution from kamyu104/LeetCode-Solutions · MIT