// Represents a time span of hours and minutes elapsed.
// Alternate implementation using only total minutes.

public class TimeSpan {
    private int totalMinutes;

    // Constructs a time span with the given interval.
    // pre: hours >= 0 && minutes >= 0
    public TimeSpan(int hours, int minutes) {
        totalMinutes = 0;
        add(hours, minutes);
    }
    
    // Adds the given interval to this time span.
    // pre: hours >= 0 && minutes >= 0
    public void add(int hours, int minutes) {
        totalMinutes += 60 * hours + minutes;
    }

    // Returns whether o is a TimeSpan representing the same
    // number of hours and minutes as this TimeSpan object.
    public boolean equals(Object o) {
        if (o instanceof TimeSpan) {
            TimeSpan other = (TimeSpan) o;
            return totalMinutes == other.totalMinutes;
        } else {   // not a TimeSpan object
            return false;
        }
    }

    // Returns a String for this time span such as "6h15m".
    public String toString() {
        return (totalMinutes / 60) + "h" + 
               (totalMinutes % 60) + "m";
    }
}