Counting Elements Python Solution with Tests

Tested Python solution for LeetCode 1426 with 26 pytest cases. Generate a practice environment with lcpy.

LeetCode 1426, Easy. Topics: Array, Hash Table. View on LeetCode.

Generate this problem as a practice environment: tested reference solution, 26 parametrized pytest cases, and a playground notebook:

lcpy gen -n 1426   # by problem number
lcpy gen -s counting_elements   # by problem name

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Problem

Given an integer array arr, count how many elements x there are, such that x + 1 is also in arr. If there are duplicates in arr, count them separately.

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Examples

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

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

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Constraints

• 1 <= arr.length <= 1000
• 0 <= arr[i] <= 1000

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Solution

Reference implementation from solution.py on GitHub, full suite in test_solution.py:

class Solution:
    # Time: O(n)
    # Space: O(n)
    def count_elements(self, arr: list[int]) -> int:
        counts: set[int] = set(arr)
        return sum(x + 1 in counts for x in arr)

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Complexity

Time	Space
O(n)	O(n)

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Tags

NeetCode All.