Day of the Year LeetCode solution in C++

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class Solution {
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 public:
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  bool leapyear(int year) {
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    return (year % 4 == 0 && (year % 100 != 0 || year % 400 == 0));
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  }
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  int dayOfYear(string date) {
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    vector<int> v;
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    int ans = 0;
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    int n = date.length();
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    for (int i = 0; i < n; i++) {
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      if (date[i] >= '0' && date[i] <= '9') {
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        ans = ans * 10 + (date[i] - '0'); // subtract '0' to get the integer value
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      } else {
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        v.push_back(ans);
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        ans = 0;
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      }
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    }
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    v.push_back(ans);             // add the last value to the vector
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    if (v.size() != 3) return -1; // error handling for invalid input
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    int year = v[0];
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    int month = v[1];
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    int day = v[2];
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    if (month == 1) return day;
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    if (month == 2) return 31 + day;
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    if (month == 3) return leapyear(year) ? 60 + day : 59 + day;
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    if (month == 4) return leapyear(year) ? 91 + day : 90 + day;
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    if (month == 5) return leapyear(year) ? 121 + day : 120 + day;
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    if (month == 6) return leapyear(year) ? 152 + day : 151 + day;
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    if (month == 7) return leapyear(year) ? 182 + day : 181 + day;
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    if (month == 8) return leapyear(year) ? 213 + day : 212 + day;
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    if (month == 9) return leapyear(year) ? 244 + day : 243 + day;
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    if (month == 10) return leapyear(year) ? 274 + day : 273 + day;
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    if (month == 11) return leapyear(year) ? 305 + day : 304 + day;
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    if (month == 12) return leapyear(year) ? 335 + day : 334 + day;
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    return -1;
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  }
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};