I am trying to implement a function which, when given two objects that represent lines, returns whether they overlap or not.

Here is how it should look like visually.

Example 1:

checkOverlap({start: 0, end: 10}, {start: 8, end: 15})

Which visually, would be:

0--------10
     8-------15
       ^ overlap

returns true.

Example 2:

checkOverlap({start: 12, end: 15}, {start: 0, end: 10})

Which visually, would be:

             12-------15   
0--------10

              no overlap

returns false.

Here is my function which works for some but not all:

function checkOverlap(lineA, lineB) {
    var result;
    for(var a in lineA) {
        for(var b in lineB) {
            if(a.end > b.start) {
                result = true;
            } else {
                result = true;
            }
        }
    }
    return result;
}

I am trying to implement a function which, when given two objects that represent lines, returns whether they overlap or not.

Here is how it should look like visually.

Example 1:

checkOverlap({start: 0, end: 10}, {start: 8, end: 15})

Which visually, would be:

0--------10
     8-------15
       ^ overlap

returns true.

Example 2:

checkOverlap({start: 12, end: 15}, {start: 0, end: 10})

Which visually, would be:

             12-------15   
0--------10

              no overlap

returns false.

Here is my function which works for some but not all:

function checkOverlap(lineA, lineB) {
    var result;
    for(var a in lineA) {
        for(var b in lineB) {
            if(a.end > b.start) {
                result = true;
            } else {
                result = true;
            }
        }
    }
    return result;
}

• javascript

• "which works for some but not all" For what input doesn't it work? From what I can tell is that it shouldn't work at all. Do a console.log(a, b) and see what the values of a and b actually are. Also, why are you assigning the same value to result in the if and else block? That means result will always be true. What do you think for (var a in lineA) does exactly? Why are you using a loop? – Felix Kling Commented Nov 12, 2016 at 21:19
• yea sorry it doesnt work, it was just outputing true and the rest of the code was not working – afkvision Commented Nov 12, 2016 at 21:22
• It was answered already: stackoverflow./questions/3269434/… – Phil B Commented Nov 21, 2018 at 16:19

3 Answers 3

Nina Scholz answer won't work, eg. a = {start: 1, end: 2}, b = {start: 0, end: 10}.

If lines {start: 0, end: 10} and {start: 10, end: 15} are count as overlapping:

 function checkOverlap(lineA, lineB) {
        return lineA.start >= lineB.start && lineA.start <= lineB.end || 
               lineA.end >= lineB.start && lineA.end <= lineB.end ||
               lineB.start >= lineA.start && lineB.start <= lineA.end || 
               lineB.end >= lineA.start && lineB.end <= lineA.end;
    }

If not:

 function checkOverlap(lineA, lineB) {
        return lineA.start > lineB.start && lineA.start < lineB.end || 
               lineA.end > lineB.start && lineA.end < lineB.end ||
               lineB.start > lineA.start && lineB.start < lineA.end || 
               lineB.end > lineA.start && lineB.end < lineA.end;
    }

The overlap must follow two conditions:

• o1.end - o2.start > 0 // >= 0 if 0-10 10-20 means overlapping

• o2.end - o1.start > 0 // >= 0 if 10-20 0-10 means overlapping

function checkOverlap(o1, o2) {
  return ((o1.end - o2.start) > 0 && (o2.end - o1.start) > 0) ? true : false;
}

console.log(checkOverlap({start: -10, end: 0}, {start: 0, end: 10}));   // false
console.log(checkOverlap({start: -20, end: -10}, {start: -5, end: 5})); // false
console.log(checkOverlap({start: 5, end: 10}, {start: 10, end: 20}));   // false
console.log(checkOverlap({start: -10, end: 0}, {start: -5, end: 5}));   // true
console.log(checkOverlap({start: -5, end: 5}, {start: -10, end: 0}));   // true
console.log(checkOverlap({start: 0, end: 10}, {start: 5, end: 15}));    // true
console.log(checkOverlap({start: 5, end: 15}, {start: 0, end: 10}));    // true

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You could check against the borders of an object.

function checkOverlap(o1, o2) {
    return (
       o1.start >= o2.start && o1.start <= o2.end ||
       o1.end >= o2.start && o1.end <= o2.end ||
       o2.start >= o1.start && o2.start <= o1.end ||
       o2.end >= o1.start && o2.end <= o1.end
    );
}

console.log(checkOverlap({start: 0, end: 10}, {start: 8, end: 15}));   // true
console.log(checkOverlap({start: 8, end: 15}, {start: 0, end: 10}));   // true
console.log(checkOverlap({start: 12, end: 15}, {start: 0, end: 10}));  // false
console.log(checkOverlap({start: 0, end: 10}, {start: 12, end: 15}));  // false
console.log(checkOverlap({start: 12, end: 15}, {start: 16, end: 17})); // false
console.log(checkOverlap({start: 16, end: 17}, {start: 12, end: 15})); // false
console.log(checkOverlap({start: 1, end: 2}, {start: 0, end: 10}));    // true
console.log(checkOverlap({start: 0, end: 10}, {start: 1, end: 2}));    // true

console.log(checkOverlap({start: 0, end: 10}, {start: 10, end: 20}));  // true
console.log(checkOverlap({start: 10, end: 20}, {start: 0, end: 10}));  // true

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