2001. Number of Pairs of Interchangeable Rectangles

https://leetcode.com/problems/number-of-pairs-of-interchangeable-rectangles

Description

You are given n rectangles represented by a 0-indexed 2D integer array rectangles, where rectangles[i] = [widthi, heighti] denotes the width and height of the ith rectangle.

Two rectangles i and j (i < j) are considered interchangeable if they have the same width-to-height ratio. More formally, two rectangles are interchangeable if widthi/heighti == widthj/heightj (using decimal division, not integer division).

Return the number of pairs of interchangeable rectangles in rectangles.

Example 1:

**Input:** rectangles = [[4,8],[3,6],[10,20],[15,30]]
**Output:** 6
**Explanation:** The following are the interchangeable pairs of rectangles by index (0-indexed):
- Rectangle 0 with rectangle 1: 4/8 == 3/6.
- Rectangle 0 with rectangle 2: 4/8 == 10/20.
- Rectangle 0 with rectangle 3: 4/8 == 15/30.
- Rectangle 1 with rectangle 2: 3/6 == 10/20.
- Rectangle 1 with rectangle 3: 3/6 == 15/30.
- Rectangle 2 with rectangle 3: 10/20 == 15/30.

Example 2:

**Input:** rectangles = [[4,5],[7,8]]
**Output:** 0
**Explanation:** There are no interchangeable pairs of rectangles.

Constraints:

• n == rectangles.length

• 1 <= n <= 105

• rectangles[i].length == 2

• 1 <= widthi, heighti <= 105

ac