1
/**
2
 * @param {string} s
3
 * @param {number} k
4
 * @return {string}
5
 */
6
var reverseStr = function (s, k) {
7
  const sArr = s.split("");
8

9
  let start = 0;
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  let end = k - 1;
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  const swapBlock = (start, end) => {
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    while (start < end) {
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      [sArr[start], sArr[end]] = [sArr[end], sArr[start]];
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      start++;
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      end--;
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    }
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  };
20

21
  while (start < end) {
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    swapBlock(start, end);
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    start = start + k * 2;
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    end = sArr[start + (k - 1)] ? start + (k - 1) : s.length - 1;
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  }
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  return sArr.join("");
29
};