Latest Time by Replacing Hidden Digits LeetCode solution in C++

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class Solution {
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 public:
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  string maximumTime(string time) {
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    // for time[0]
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    // if both characters of hour is ?, then hour is 23 then time[0] should be
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    // '2'("??:3?)". if 2nd character of hour is <= 3, then hour can be in 20s
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    // then time[0] should be '2'. if 2nd character of hour is >3, then hour can
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    // only be in 10s  then time[0] should be '1'.
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    if (time[0] == '?') time[0] = (time[1] <= '3' || time[1] == '?') ? '2' : '1';
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    // if 1st character of hour is 0 or 1, then hour can be 09 or 19 then
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    // time[1] should be '9'. if 1st character of hour is 2, then hour can be 23
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    // then time[1] should be '3'.
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    if (time[1] == '?') time[1] = time[0] == '2' ? '3' : '9';
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    // if both characters of minute is ? then minute is 59, or only 4th
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    // character is ? then 5_ so time[3] is always '5'.
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    if (time[3] == '?') time[3] = '5';
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    // if 2nd character of minute is ?, then time[4] is '9'.
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    if (time[4] == '?') time[4] = '9';
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    return time;
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  }
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};