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/**
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 * @param {number[][]} intervals
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 * @return {number}
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 */
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var intersectionSizeTwo = function (intervals) {
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  const sortedIntervals = intervals.sort(sortEndsThenStarts);
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  let currentTail = [];
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  let answer = 0;
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  sortedIntervals.forEach((interval) => {
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    const start = interval[0];
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    const end = interval[1];
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    const startPoint = currentTail[0];
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    const lastPoint = currentTail[1];
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    if (!currentTail.length || lastPoint < start) {
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      currentTail = [end - 1, end];
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      answer += 2;
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    } else if (startPoint < start) {
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      currentTail = [currentTail[1], end];
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      answer += 1;
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    }
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  });
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  return answer;
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};
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function sortEndsThenStarts(intervalA, intervalB) {
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  return intervalA[1] < intervalB[1] ? -1 : 1;
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}