Minimum Number of Swaps to Make the String Balanced LeetCode solution in C++

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class Solution {
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 public:
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  int minSwaps(string s) {
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    int ans = 0;
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    stack<char> stack;
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    for (int i = 0; i < s.length(); i++) {
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      if (s[i] == '[') {
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        stack.push(s[i]);
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      }
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      if (s[i] == ']' && stack.size() != 0 && stack.top() == '[') {
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        stack.pop();
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      }
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    }
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    ans = stack.size();
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    if (ans % 2 == 0)
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      return ans / 2;
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    else
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      return (ans + 1) / 2;
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  }
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};