"""
Given an integer array arr, count element x such that x + 1 is also in arr.

If there're duplicates in arr, count them seperately.

    Example 1:
    Input: arr = [1,2,3]
    Output: 2
    Explanation: 1 and 2 are counted cause 2 and 3 are in arr.

    Example 2:
    Input: arr = [1,1,3,3,5,5,7,7]
    Output: 0
    Explanation: No numbers are counted, cause there's no 2, 4, 6, or 8 in arr.

    Example 3:
    Input: arr = [1,3,2,3,5,0]
    Output: 3
    Explanation: 0, 1 and 2 are counted cause 1, 2 and 3 are in arr.

    Example 4:
    Input: arr = [1,1,2,2]
    Output: 2
    Explanation: Two 1s are counted cause 2 is in arr.
"""


class Solution(object):
    def countElements(self, arr):
        """
        :type arr: List[int]
        :rtype: int
        """

        if len(arr) == 0:
            return 0

        orig_set = set(arr)

        counter =0

        for num in arr:
            if num in orig_set and num+1 in orig_set:
                counter += 1

        return counter


sol_instance = Solution()

x = sol_instance.countElements([1,1,2,2])

print(x, "x")
