Minimum Swaps to Make Strings Equal LeetCode solution in C++

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class Solution {
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 public:
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  int minimumSwap(string s1, string s2) {
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    int n = s1.size();
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    int cnt1 = 0, cnt2 = 0, i = 0;
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    while (i < n) {
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      int x = s1[i];
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      int y = s2[i++];
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      if (x == 'x' and y == 'y') cnt1++;
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      if (x == 'y' and y == 'x') cnt2++;
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    }
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    if ((cnt1 + cnt2) % 2 == 1) return -1;
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    return (cnt1 / 2) + (cnt2 / 2) + (cnt1 % 2 + cnt2 % 2);
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  }
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};