Number of Good Pairs Python Solution

Tested Python solution for LeetCode 1512 with 16 pytest cases. Generate a practice environment with lcpy.

LeetCode 1512, Easy. Topics: Array, Hash Table, Math, Counting. View on LeetCode.

Generate this problem as a practice environment: tested reference solution, 16 parametrized pytest cases, and a playground notebook:

lcpy gen -n 1512   # by problem number
lcpy gen -s number_of_good_pairs   # by problem name

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Problem

Given an array of integers nums, return the number of good pairs.

A pair (i, j) is called good if nums[i] == nums[j] and i < j.

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Examples

Input: nums = [1,2,3,1,1,3]
Output: 4

Explanation: There are 4 good pairs (0,3), (0,4), (3,4), (2,5) 0-indexed.

Input: nums = [1,1,1,1]
Output: 6

Explanation: Each pair in the array are good.

Input: nums = [1,2,3]
Output: 0

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Constraints

• 1 <= nums.length <= 100
• 1 <= nums[i] <= 100

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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 num_identical_pairs(self, nums: list[int]) -> int:
        counts: dict[int, int] = {}
        result = 0
        for num in nums:
            seen = counts.get(num, 0)
            result += seen
            counts[num] = seen + 1
        return result

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Complexity

Time	Space
O(n)	O(n)

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Tags

NeetCode All.