I think one approrach to use Javascript string split.

    const [time, period] = time12h.split(/(AM|PM)/);
    const [hours, minutes, seconds] = time.split(':');
    const hours24h = period === 'PM' && hours !== '12' ? parseInt(hours) + 12 : hours === '12' && period === 'AM' ? '00' : hours;
    return `${hours24h}:${minutes}:${seconds}`;

Java

    public static String timeConversion(String s) {
        if (s.charAt(8) == 'P') {
            if (Integer.valueOf(s.substring(0, 2)) < 12) {
              String res = String.valueOf(Integer.valueOf(s.substring(0, 2)) + 12);
                res = res.concat(s.substring(2, 8));
                return res;
            } else return s.substring(0, 8);            
        } else {
            if (Integer.valueOf(s.substring(0, 2)) < 12) {
                return s.substring(0, 8);
            } else {
                String res = "00";
                res = res.concat(s.substring(2, 8));
                return res;
            }  
        }
    }

C# Code

public static string timeConversion(string s) { var time = DateTime.Parse(s); return time.ToString("HH:mm:ss"); }

I tried the most manual approach to do these. I am not sure if these the best way to do it . PLease someone try and lets discuss if these is an acceptable answer for interviewer or not . string timeConversion(string s) { vector result; stringstream ss(s); string strToken;

while(getline(ss,strToken,':')){
    result.push_back(strToken);
}

if(result[2][2] == 'A'){
    if(result[0] == "12"){
        result[0] = "00";
    }
}
else{
    int value = stoi(result[0]);
    if(value >= 1 && value <= 11){
        result[0] = to_string(12 + value);
    }
}

string ans = result[0] + ":" + result[1] + ":" + result[2].erase(4-2);
return ans;  

}

public static String timeConversion(String s) {
// Write your code here

return LocalTime.parse(s, DateTimeFormatter.ofPattern("hh:mm:ssa", Locale.US))
.format(DateTimeFormatter.ofPattern("HH:mm:ss"));



}