1
var RLEIterator = function (encoding) {
2
  this.encoding = encoding;
3
  // Pointer to count index
4
  this.index = 0;
5
};
6

7
RLEIterator.prototype.next = function (n) {
8
  while (n > 0) {
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    // Move to next count index when the current index is 0
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    if (this.encoding[this.index] === 0) this.index += 2;
11

12
    // Too many calls to next, return -1
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    if (this.index >= this.encoding.length) return -1;
14

15
    // n goes completely into count
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    if (n <= this.encoding[this.index]) {
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      this.encoding[this.index] -= n;
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      n = 0;
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      // count goes completely into n
20
    } else if (n > this.encoding[this.index]) {
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      n -= this.encoding[this.index];
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      this.encoding[this.index] = 0;
23
    }
24
  }
25

26
  return this.encoding[this.index + 1];
27
};