C++: simple O(1) time O(1) space solution
```\nclass Solution {\npublic:\n    /// 0 ms, faster than 100.00% of C++\n    /// 6 MB, less than 11.60% of C++\n    int numberOfRounds(string st, string ft)\n 
```\nclass Solution {\npublic:\n    /// 0 ms, faster than 100.00% of C++\n    /// 6 MB, less than 11.60% of C++\n    int numberOfRounds(string st, string ft)\n    {\n\t    /// both start and finish will be = hours * 60 + minutes\n        int start = ((st[0]-\'0\')*10 + (st[1]-\'0\')) * 60 + ((st[3]-\'0\')*10 + (st[4]-\'0\'));\n        int finish = ((ft[0]-\'0\')*10 + (ft[1]-\'0\')) * 60 + ((ft[3]-\'0\')*10 + (ft[4]-\'0\'));\n\t\t/// if finish is earlier than the start => add a full day\n        if (finish < start)\n            finish += 24*60;\n\t\t/// make sure that we use 15-minute intervals\n        if (start % 15)\n            start += 15 - (start % 15);\n        if (finish % 15)\n            finish -= (start % 15);\n        return (finish - start) / 15;\n    }\n};
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