Find the Longest Valid Obstacle Course at Each Position LeetCode solution in JavaScript

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var longestObstacleCourseAtEachPosition = function (obstacles) {
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  var n = obstacles.length;
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  var lis = [];
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  var res = new Array(n).fill(0);
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  for (var i = 0; i < n; i++) {
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    if (lis.length > 0 && obstacles[i] >= lis[lis.length - 1]) {
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      lis.push(obstacles[i]);
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      res[i] = lis.length;
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    } else {
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      // find the upper bound
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      var l = 0;
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      var r = lis.length;
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      while (l <= r) {
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        var mid = Math.floor((l + r) / 2);
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        if (lis[mid] <= obstacles[i]) {
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          l = mid + 1;
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        } else {
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          r = mid - 1;
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        }
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      }
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      lis[l] = obstacles[i];
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      res[i] = l + 1;
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    }
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  }
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  return res;
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};