Day 7 - Counting elements

Solution.py

# https://leetcode.com/explore/challenge/card/30-day-leetcoding-challenge/528/week-1/3289/
class Solution:
    def countElements(self, arr: List[int]) -> int:
        s = set(arr)
        c = 0
        for n in arr:
            if n + 1 in s:
                c += 1
        return c