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/**
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 * @param {number} n
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 * @param {number[]} blacklist
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 */
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var Solution = function (n, blacklist) {
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  this.space = n - blacklist.length;
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  this.map = {};
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  blacklist.forEach((b, i) => {
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    const next = this.space + i;
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    const head = this.map[b] === undefined ? b : this.map[b];
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    const tail = this.map[next] === undefined ? next : this.map[next];
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    this.map[head] = tail;
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    this.map[tail] = head;
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  });
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};
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/**
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 * @return {number}
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 */
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Solution.prototype.pick = function () {
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  const result = Math.floor(Math.random() * this.space);
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  return this.map[result] || result;
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};
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/**
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 * Your Solution object will be instantiated and called as such:
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 * var obj = new Solution(n, blacklist)
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 * var param_1 = obj.pick()
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 */