1
var convert = function (s, numRows) {
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  let result = [];
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  let row = 0;
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  let goingUp = false;
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  for (let i = 0; i < s.length; i++) {
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    result[row] = (result[row] || "") + s[i]; // append letter to active row
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    if (goingUp) {
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      row--;
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      if (row === 0) goingUp = false; // reverse direction if goingUp and reaching top
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    } else {
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      row++;
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      if (row === numRows - 1) goingUp = true; // reverse direction after reaching bottom
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    }
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  }
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  return result.join("");
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};