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The purpose here is to find if there is a conflict in the given set of start and end times of the meeting time slots listed.

Input: Start and end times of meetings

Output: True / False for conflicts

package code.Misc;

import java.util.ArrayList;

public class Calendar {

static int time [] = new int[1440];

public static void main(String args[]){

    String s[] =   {"15:30","1:30","1:15","15:00"};
    String e[] = {"18:35","13:28","1:30","15:29"};

    System.out.println(scheduler(s, e));
}

public static int calculateMinute(int hour, int minute){
        return hour*60+minute;
}

public static boolean timeClashChecker(int start, int end){
        for(int i=start;i<=end;i++){
            if(i==end){
                time[i] =  -1;
            }
            else if(time[i]==1){
                return false;
            }
            else if(time[i]==-1){
                time[i]=1;
            }
            else{
                time[i]=1;
            }
        }
    return true;
}
public static int parser(String time){
    String [] timeParts = time.split(":");
    int hour = Integer.parseInt(timeParts[0].trim());
    int minute = Integer.parseInt(timeParts[1].trim());

    return calculateMinute(hour,minute);
}
public static boolean scheduler(String start[], String end[]){

    for(int i=0;i<start.length;i++){
        int startMeeting = parser(start[i]);
        int endMeeting = parser(end[i]);
        boolean result = timeClashChecker(startMeeting,endMeeting);
        if(result == false){ //clash check
            return false;
        }
    }
    return true;
}
}
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  • 1
    \$\begingroup\$ do not make class name like calendar as it already exists because if in any other program if you want to call default calendar class, might end up calling this or vice versa , may cause you trouble :) \$\endgroup\$
    – bananas
    Jun 26, 2016 at 10:43

2 Answers 2

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A couple of things that would be good to point out:

  • It appears that your code only checks the clash between the start and end time. If the start time is always bigger than the end time, in theory it should never clash.

    for(int i=0;i<start.length;i++){
        int startMeeting = parser(start[i]);
        int endMeeting = parser(end[i]);
        boolean result = timeClashChecker(startMeeting,endMeeting);
        if(result == false){ //clash check
            return false;
        }
    }
    

    might be replaced with:

    for(int i=0;i<start.length;i++){
        int startMeeting = parser(start[i]);
        int endMeeting = parser(end[i]);
        for(int e = 0; e < end.length; e++){
            if(e == i) continue;
            int meetingEnd = parser(end[e]);
            if(meetingEnd > startMeeting && meetingEnd < endMeeting) return true;
        }
    
        for(int s = 0; s < start.length; s++){
            if(s == i) continue;
            int meetingStart = parser(start[s]);
            if(meetingStart > startMeeting && meetingStart < endMeeting) return true;
        }
    
    }
    

This way the end of each meeting is checked with each starting time. If there is a clash with any of them, it should detect it. It also checks if each starting time of another is also between a meeting.

  • If you make the change above, your timeClashChecker method is unnecessary.
  • Some of the method names are not entirely helpful.parser could become parseTime, and scheduler could be changed to doesClash, especially seeing it doesn't do any of the scheduling itself.
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Using model classes

It's not easy to manage a pair of String values to determine if the timings they represent overlap. You have to:

  1. Ensure both arrays are of the same length, and the values lined up,
  2. Interpret and validate the values (parser(String) plus calculateMinute(int, int)),
  3. Deal with int values that you need to loop through, and finally
  4. Require an intermediary time[] loop that stores... 1440 minutes in a day to record clashes.

Java 8 java.time.* or Joda-Time

If you are on Java 8, there's the java.time.* APIs that you can use to model these times into nicer classes to work on. If you are not, you can still rely on Joda-Time for its selection of chronology-related classes.

For example, on Java 8, you can have a simple model class like:

public class TimeSlot {
    private final LocalTime start;
    private final LocalTime end;

    public TimeSlot(LocalTime start, LocalTime end) {
        // assuming we don't need additional validation here
        this.start = start;
        this.end = end;
    }

    // getters - getStart(), getEnd() - omitted for brevity
}

Then, given a List<TimeSlot>, you can sort through them and compare the start and end times:

private static boolean hasClashes(Collection<TimeSlot> timeSlots) {
    // materialize into another collection to not affect the input
    List<TimeSlot> inputs = new ArrayList<>(timeSlots);
    Collections.sort(inputs, Comparator.comparing(TimeSlot::getStart)
                                .thenComparing(TimeSlot::getEnd));
    TimeSlot previous = inputs.get(0); // assuming at least one
    for (int i = 1; i < inputs.size(); i++) {
        TimeSlot current = inputs.get(i);
        if (!current.getStart().isAfter(previous.getEnd())) {
            return false;
        } else {
            previous = current;
        }
    }
    return true;
}
  1. sort() using a Comparator that uses TimeSlot.getStart() as a method reference for the first comparison, thenComparing() the end time if two TimeSlots have the same start time.
  2. Loop through the sorted List and compare using LocalTime.isAfter(LocalTime), which is easier to read and understand.
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