Count Numbers with Unique Digits LeetCode solution in JavaScript

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/**
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 * @param {number} n
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 * @return {number}
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 */
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var countNumbersWithUniqueDigits = function (n) {
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  if (n == 0) return 1;
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  let res = 1;
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  let k = 0;
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  for (let i = 1; i <= n; i++) {
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    k = 1;
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    for (let j = 0; j < i; j++) {
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      if (j == 0) {
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        k *= 9 - j;
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      } else {
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        k *= 10 - j;
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      }
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    }
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    res += k;
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  }
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  return res;
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};