1920 Special Semester Q7

[wenshienyap]

Summary

Hi! I'm not too sure on how to go about solving this question, I think what confused me was how to initialise the points for the circle objects to be created. If anyone has any suggested solutions I would love to know how you guys did it!

Screenshots (if any):

[gracefour11]

there's a pattern in which the different circle's centre coordinates are created.

if it's getCircles(10) --> (1,10) , (2,9) ...... (9,2), (10,1)

since you can't use for loops or helper class, u can use streams! (Hint: IntStream)

Hope this helps!

[chinjuanlee]

you can try using intStream.mapToObj(x -> new Circle(..........))

[gableejh]

i did this return Stream.iterate(1, x -> x <= n, x -> x + 1).map(x -> new Circle(new Point(x, n + 1 - x))).collect(Collectors.toList());

[wenshienyap]

Actually, was wondering, is there a difference between using IntStream and Stream? not really right, like since we know that our stream will be all ints?

[chamath2030]

all the same so long as u can produce the right output

[ruthkangyr]

you can try using intStream.mapToObj(x -> new Circle(..........))

I know using map only will be wrong but why is it the case where we have to use mapToObj?

[seannzx]

you can try using intStream.mapToObj(x -> new Circle(..........))

I know using map only will be wrong but why is it the case where we have to use mapToObj?

IntStream has a Stream type of Integer. Since you want the resulting Stream to store Circle, this IntStream has to be mapped to an appropriate Stream<Circle> via mapToObj

[seannzx]

This is how I did it

List<Circle> getCircles(int n) {
        return Stream.iterate(new Circle(new Point(1, n)), circle -> new Circle(new Point(circle.centre.x + 1, circle.centre.y - 1)))
                    .limit(n)
                    .collect(Collectors.toList());
}

``

[chooweixiang98]

[e0543492]

[rljw]

I had a slightly different approach to iteration that does not require the use of .limit(), hope this offers a new perspective!

List<Circle> getCircles(int n) {
       return Stream.iterate(1, x -> x < n + 1, x -> x+1)
       .map(x -> new Point(n - x + 1, x))
       .map(x -> new Circle(x))
       .collect(Collectors.toList());
  
 }

Nonetheless both ways should still work. You can also use IntStream as the others have mentioned, but remember to use mapToObj instead of the usual map (map would give an error)

[marvinljw]

I did this method.

Stream.rangeClosed(1,n)
.map(x -> new Circle(new Point(x,n-x+1)))
.collect(Collectors.toList());

[Deshun99]

i did this, hope it helps

List getCircles(int n) {
return Stream.iterate(1, x -> n + 1, x -> x + 1).
map(x -> new Circle(new Point(x, n + 1 - x)).
collect(Collectors.toList());
}

[zhiqixn]

Hi, I'm not sure if there were IntStream implementations for this question so here's my method for this question! :-)

[danieltwh]

you can try using intStream.mapToObj(x -> new Circle(..........))

I know using map only will be wrong but why is it the case where we have to use mapToObj?

Hey @ruthkangyr, IntStream's .map() takes in an IntUnaryOperator. Hence, the function provided must return an Integer. This makes sense as IntStream is a stream of integers (Note that it is not a Stream<Integer>. It is a separate class altogether).

Since you want a Stream, then you would have to call .mapToObject( x -> new Circle(...)). Alternatively, you can also do intStream.boxed() to convert an IntStream to a Stream<Integer> before calling .map(x -> new Circle(...)).

Hope this help! :)

[Herrekt]

Hi, I'm not sure if there were IntStream implementations for this question so here's my method for this question! :-)

IntStream would need to be mapped to Object (via mapToObj) I think, as normal outputs for IntStream would still be integers.