Maximum Points in an Archery Competition LeetCode solution in JavaScript

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var maximumBobPoints = function (numArrows, aliceArrows) {
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  let max = 0,
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    n = aliceArrows.length,
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    res;
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  backtrack(numArrows, 0, 0, Array(n).fill(0));
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  return res;
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  function backtrack(arrows, idx, points, bobArrows) {
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    if (idx === n || arrows === 0) {
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      let origVal = bobArrows[n - 1];
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      if (arrows > 0) bobArrows[n - 1] += arrows; // put extra arrows in any slot
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      if (points > max) {
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        max = points;
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        res = [...bobArrows];
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      }
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      bobArrows[n - 1] = origVal;
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      return;
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    }
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    backtrack(arrows, idx + 1, points, bobArrows); // don't use any arrows
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    if (aliceArrows[idx] + 1 <= arrows) {
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      // use aliceArrows[idx] + 1 arrows to gain idx points
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      bobArrows[idx] = aliceArrows[idx] + 1;
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      backtrack(
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        arrows - (aliceArrows[idx] + 1),
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        idx + 1,
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        points + idx,
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        bobArrows
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      );
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      bobArrows[idx] = 0;
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    }
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  }
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};