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class Solution {
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 public:
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  int secondHighest(string s) {
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    // support variables
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    int res[2] = {-1, -1};
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    // parsing s
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    for (char c : s) {
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      // considering only numerical characters
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      if (c >= '0' && c <= '9') {
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        // normalising c
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        c -= '0';
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        // updating res
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        if (c > res[0]) {
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          res[1] = res[0];
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          res[0] = c;
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        } else if (c != res[0] && c > res[1])
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          res[1] = c;
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      }
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    }
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    return res[1];
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  }
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};