Grokking the Coding Interview: Patterns for Coding Questions
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Number of Good Pairs (easy)
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Problem Statement

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.

Example 1:

Input: nums = [1,2,3,1,1,3]
Output: 4
Explanation: There are 4 good pairs, here are the indices: (0,3), (0,4), (3,4), (2,5).

Example 2:

Input: nums = [1,1,1,1]
Output: 6
Explanation: Each pair in the array is a 'good pair'.

Example 3:

Input: words = nums = [1,2,3]
Output: 0
Explanation: No number is repeating.

Constraints:

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

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Python3
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