Number of Good Pairs

EasyArrays & Hashinghashing

Solve this the way you would in the interview: out loud, on a timer, with an AI interviewer asking follow-ups while you code. You get a scored report at the end.

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Problem

Given an integer array nums, count the index pairs (i, j) with i < j and nums[i] == nums[j]. Return that count. An O(n) solution with a frequency map is expected.

Examples

Input: nums = [1,2,3,1,1,3]
Output: 4
The pairs are (0,3), (0,4), (3,4) for the value 1 and (2,5) for the value 3.
Input: nums = [1,1,1,1]
Output: 6
Any two of the four indices form a pair: 4 * 3 / 2 = 6.
Input: nums = [1,2,3]
Output: 0
No value repeats.

Constraints

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

What the interviewer grades

A correct solution is one of five scores. The report also grades problem understanding (did you clarify inputs and edge cases before coding), problem solving, communication while you work, code quality, and testing. See a sample report, or read up on the pattern in the lessons.

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