Describe the Painting LeetCode solution in JavaScript

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/**
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 * @param {number[][]} segments
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 * @return {number[][]}
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 */
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var splitPainting = function (segments) {
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  const arr = [];
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  segments.forEach(([start, end, val]) => {
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    arr.push([start, val]);
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    arr.push([end, -val]);
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  });
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  arr.sort((i, j) => i[0] - j[0]);
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  const ans = [];
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  let currVal = 0,
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    prevTime;
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  arr.forEach(([time, val]) => {
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    if (prevTime !== undefined && currVal && prevTime !== time)
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      ans.push([prevTime, time, currVal]);
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    currVal += val;
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    prevTime = time;
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  });
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  return ans;
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};