New 21 Game LeetCode solution in JavaScript

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var new21Game = function (n, k, maxPts) {
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  if (k + maxPts <= n || k === 0) return 1;
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  let dp = [];
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  dp[0] = 1;
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  dp[1] = 1 / maxPts;
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  for (let i = 2; i <= n; i++) {
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    dp[i] = 0;
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    if (i <= k) {
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      dp[i] = (1 + 1 / maxPts) * dp[i - 1];
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    } else {
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      dp[i] = dp[i - 1];
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    }
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    if (i > maxPts) {
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      dp[i] -= dp[i - maxPts - 1] / maxPts;
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    }
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  }
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  return dp.reduce((acc, cur, idx) => {
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    if (idx >= k) {
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      acc += cur;
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    }
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    return acc;
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  }, 0);
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};