Check If N and Its Double Exist

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 arr, return true if there are two **different indices** i and j such that arr[i] == 2 * arr[j], and false otherwise. The indices must differ, so a single 0 does not pair with itself — but two zeros do. Negative values count too (-4 is double -2). An O(n) solution with a hash set is expected.

Examples

Input: arr = [10,2,5,3]
Output: true
10 at index 0 is double 5 at index 2.
Input: arr = [3,1,7,11]
Output: false
No element is twice another element.
Input: arr = [0,5,0]
Output: true
The zeros at indices 0 and 2 satisfy 0 == 2 * 0.

Constraints

  • 2 <= arr.length <= 500
  • -1000 <= arr[i] <= 1000
  • `i != j` is required.

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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