Gas Station LeetCode solution in JavaScript

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var canCompleteCircuit = function (gas, cost) {
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  const len = gas.length;
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  // scan forward from the current index
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  const scan = (i) => {
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    let numTries = 0;
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    let tank = 0;
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    let c = 0;
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    while (numTries <= len) {
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      tank -= c;
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      if (tank < 0) return -1;
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      // if we made it back around, and we have gas, return the index, we made it!
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      if (numTries === len && tank >= 0) {
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        return i;
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      }
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      tank += gas[i];
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      c = cost[i];
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      i++;
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      if (i === len) i = 0; // if we hit the end, bounce back to zero
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      numTries++;
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    }
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    return -1;
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  };
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  for (let i = 0; i < len; i++) {
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    if (!gas[i]) continue; // no gas / zero gas so let's just move on
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    let index = scan(i);
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    if (~index) return index; // if it's not -1, return it
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  }
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  return -1;
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};