Count Number of Rectangles Containing Each Point LeetCode solution in JavaScript

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var countRectangles = function (rectangles, points) {
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  let buckets = Array(101)
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    .fill(0)
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    .map(() => []);
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  for (let [x, y] of rectangles) {
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    buckets[y].push(x);
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  }
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  for (let i = 0; i < 101; i++) buckets[i].sort((a, b) => a - b);
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  let res = [];
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  for (let point of points) {
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    let sum = 0;
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    for (let j = point[1]; j < 101; j++) {
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      // lowest index >= point[0]
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      let index = lower_bound(buckets[j], point[0]);
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      sum += buckets[j].length - index;
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    }
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    res.push(sum);
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  }
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  return res;
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  function lower_bound(arr, targ) {
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    let low = 0,
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      high = arr.length;
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    while (low < high) {
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      let mid = Math.floor((low + high) / 2);
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      if (arr[mid] >= targ) high = mid;
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      else low = mid + 1;
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    }
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    return low;
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  }
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};