Nth Magical Number LeetCode solution in JavaScript

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/**
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 * @param {number} N
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 * @param {number} A
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 * @param {number} B
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 * @return {number}
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 */
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var nthMagicalNumber = function (N, A, B) {
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  var temp;
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  if (B > A) {
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    temp = A;
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    A = B;
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    B = temp;
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  }
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  //A is bigger
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  var shareFreq = (A + B) / GCD(A, B) - 1;
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  var numShares = Math.floor(N / shareFreq);
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  var superN = N + numShares;
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  //X+Y = superN
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  var X = Math.ceil((superN * B) / (A + B));
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  var Y = Math.ceil(superN - (superN * B) / (A + B));
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  var mod = 10 ** 9 + 7;
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  if (X * A <= Y * B) return (X * A) % mod;
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  else return (Y * B) % mod;
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};
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var GCD = function (x, y) {
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  while (y != 0) {
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    var t = y;
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    y = x % y;
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    x = t;
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  }
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  return x;
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};