1
var PeekingIterator = function (iterator) {
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  this.iterator = iterator;
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  this.curr = iterator.next();
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};
5

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PeekingIterator.prototype.peek = function () {
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  return this.curr;
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};
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PeekingIterator.prototype.next = function () {
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  let temp = this.curr;
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  this.curr = this.iterator.next();
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  return temp;
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};
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PeekingIterator.prototype.hasNext = function () {
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  return this.curr > 0; // the input iterator return -100000000 when next() after it run out of members, instead of return undefined.
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};