1
var Solution = function (nums) {
2
  this.map = nums.reduce((result, num, index) => {
3
    const value = result.get(num) ?? [];
4

5
    value.push(index);
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    result.set(num, value);
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    return result;
8
  }, new Map());
9
};
10

11
Solution.prototype.pick = function (target) {
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  const pick = this.map.get(target);
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  const random = (Math.random() * pick.length) | 0;
14

15
  return pick[random];
16
};