Number of Pairs of Interchangeable Rectangles LeetCode solution in JavaScript

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/**
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 * @param {number[][]} rectangles
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 * @return {number}
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 */
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var interchangeableRectangles = function (rectangles) {
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  let m = new Map();
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  for (let i = 0; i < rectangles.length; i++) {
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    let width = rectangles[i][0];
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    let height = rectangles[i][1];
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    let aspectRatio = width / height;
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    if (!m.has(aspectRatio)) {
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      m.set(aspectRatio, 1);
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    } else {
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      m.set(aspectRatio, m.get(aspectRatio) + 1);
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    }
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  }
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  let ans = 0;
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  m.forEach((value) => {
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    if (value > 1) {
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      let n = value - 1;
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      ans += (n * (n + 1)) / 2;
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    }
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  });
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  return ans;
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};