Minimum Speed to Arrive on Time LeetCode solution in JavaScript

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var minSpeedOnTime = function (dist, hour) {
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  let left = 1,
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    right = 10000000,
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    speed,
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    sum,
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    ans = -1;
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  while (left <= right) {
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    //We need to return the minimum positive integer speed (in kilometers per hour) that all the trains must travel. So speed will always be an integer ranging from 1 to 10000000 as per the question description.
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    speed = left + Math.floor((right - left) / 2);
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    sum = 0;
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    for (let i = 0; i < dist.length - 1; i++) {
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      sum += Math.ceil(dist[i] / speed);
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    }
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    sum += dist[dist.length - 1] / speed; //For the last train we need not to do Math.ceil
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    if (sum <= hour) {
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      //sum(time taken is less than the required time, so it can be our answer, but we will keep looking for the another smaller speed until left<=right)
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      ans = speed;
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      right = speed - 1;
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    } else {
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      left = speed + 1;
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    }
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  }
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  return ans;
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};