Minimum Number of Swaps to Make the Binary String Alternating LeetCode solution in Java

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class Solution {
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  public int minSwaps(String s) {
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    int cntZero = 0, cntOne = 0;
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    for (char ch : s.toCharArray()) {
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      if (ch == '0') cntZero++;
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      else cntOne++;
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    }
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    // Invalid
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    if (Math.abs(cntOne - cntZero) > 1) return -1;
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    if (cntOne > cntZero) { // one must be at even posotion
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      return countSwaps(s, '1');
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    } else if (cntOne < cntZero) {
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      return countSwaps(s, '0'); // zero must be at even position
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    }
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    return Math.min(countSwaps(s, '0'), countSwaps(s, '1'));
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  }
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  // wrong count
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  private int countSwaps(String s, char start) {
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    int wrongPosition = 0;
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    for (int i = 0; i < s.length(); i += 2) {
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      if (s.charAt(i) != start) wrongPosition++;
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    }
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    return wrongPosition;
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  }
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}