Determine Whether Two Date Ranges Overlap?

Question

Given two date ranges, what is the simplest or most efficient way to determine whether the two date ranges overlap?As an example, suppose we have ranges denoted by DateTime variables `StartDate1` to `EndDate1` *and* `StartDate2` to `EndDate2`.

Answer 1

For OOP, the DateTime variable (presuming it is an object) can be compared outright; It's class perhaps overloads the basic comparison operators < , >, and ==

Dates like these are typically considered long integers which contain the number of milliseconds or system ticks from a starting point called the EPOCH.

anyways, given this functionality, the overlap can be tested by comparing

(start1 < start2) AND (stop1 < start2)

It should also be guaranteed that the start1 < start2....

Here's a java routine that does this algorithm:

class OverlapIntervals

{

public static void main(String args[])

{

long start1, start2, stop1, stop2;

//UNCOMMENT the one you want to test... then recompile and run

start1=10; stop1=20; start2=15; stop2 = 30; // they overlap

//start1=10; stop1=15; start2=20; stop2 = 25; // they do not overlap

//start1 = 15; stop1 = 30; start2 = 10; stop2 = 20; // they overlap

//start1 = 20; stop1 = 25; start2=10; stop2=15; // they do not overlap

//start1 = 25; stop1=30; start2= 15; stop2= 40; // they overlap; in fact one is subset of the other

// start1 = 5; stop1 = 7; start2 = 25; stop2=28; they do not overlap

//start1 = 10; stop1 = 15; start2=15; stop2=20; //they overlap at exactly one point

//IF NECESSARY, swaps the pairs so that start1 < start2

if (start2 < start1)

{

long startTemp = start1;

long stopTemp = stop1;

start1 = start2;

stop1 = stop2;

start2 = startTemp;

stop2 = stopTemp;

}

// Is it considered OVERLAP if stop1 == start2 ???? see last test case above

// if NOT, then you must change the last condition to stop1 <= start2

if ((start1 < start2) && ( stop1 < start2))

{

System.out.println(" They do not overlap ");

//sets the return value here to reflect they do not overlap

}

else

{

System.out.println(" they overlap ");

//sets the return value here to reflect they overlap

}

//return

} //main

} //class