直接暴力枚举

class Solution {
public:
    bool check(string time,string res){
        for(int i = 0;i < 5;i++){
            if(time[i] == res[i] || time[i] == '?') 
                continue;
            return false;
        }
        return true;
    }
    string maximumTime(string time) {
        for(int i = 23;i >= 0;i--){
            for(int j = 59;j >= 0;j--){
                char res[10];
                sprintf(res,"%02d:%02d",i,j);
                if(check(time,res))
                    return res;
            }
        }
        return "";
    }
};