79-change-time-format

public String changeTimeFormat(String strTime) {
    //find first 2 digits before colon, convert to number
    String strHours = strTime.substringBefore(':');
    Integer intHours = Integer.valueOf(strHours);
    String minutes = strTime.substringAfter(':');
    String ampm;
    
    //00 hours to 12am
    if (strHours == '00'){
        ampm = 'AM';
        intHours = intHours + 12;
        strHours = String.valueOf(intHours);
    }
    // before 10am need to add a leading 0
    else if (intHours < 10 ){
        ampm = 'AM';         
        strHours = '0' + String.valueOf(intHours);
    }
    else if (intHours < 12){
        ampm = 'AM';
    }
    //midday just add PM
    else if (intHours == 12){
        ampm = 'PM';
    }
    //before 10pm need to add a leading 0
    // subtract 12 hours to convert 24hr to 12hr
    else if (intHours < 22){
        ampm = 'PM';
        intHours = intHours - 12;
        strHours = '0' + String.valueOf(intHours); 
    }
    else {
        ampm = 'PM';
        intHours = intHours - 12;
        strHours = String.valueOf(intHours);
    }
    return strHours + ':' + minutes + ' '+ ampm;
}