Minimum Swaps to Make Strings Equal LeetCode solution in JavaScript

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var minimumSwap = function (s1, s2) {
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  let count1 = 0;
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  let count2 = 0;
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  for (let i in s1) {
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    if (s1[i] === "x" && s2[i] === "y") {
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      count1++;
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    }
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    if (s1[i] === "y" && s2[i] === "x") {
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      count2++;
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    }
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  }
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  let ans = Math.floor(count1 / 2) + Math.floor(count2 / 2);
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  if (count1 % 2 === 0 && count2 % 2 === 0) {
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    return ans;
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  } else if (count1 % 2 !== 0 && count2 % 2 !== 0) {
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    return ans + 2;
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  } else {
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    return -1;
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  }
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};