CODEWITHSUNDEEP
iosmathmappingsquare-root
pbertsch
pbertsch

Reputation: 330

implementing cantor pairing function in iOS

I have a implementation of the Cantor Pairing Function in Java which I wrote 2 years ago. Now then I'm moving more to iOS I need the same thing in Objective-C.

The problem is, at least from my point of view, in Java I had to implement a BigSqrt Class which I did by my self. Because theoreticaly I can now Pair any size of number.

Because I am new to iOS I really do not know if I have to implement all the things again for objective-C or is there something already implemented. If so, could someone give me a hint where to start implementing the Cantor Pairing function for any size of "Integer" in Objective-C ?

thanks

Upvotes: 2

Views: 2272

Answers (2)

2snacc
2snacc

Reputation: 6353

I used this to set tags on tableview cells:

NSUInteger cantorPair(NSIndexPath *indexPath)
{
    NSUInteger x = indexPath.section;
    NSUInteger y = indexPath.row;
    return ((x + y) * (x + y + 1)) / 2 + y;
}


NSIndexPath *reverseCantorPair(NSUInteger z)
{
    NSUInteger t = floor((-1.0f + sqrt(1.0f + 8.0f * z))/2.0f);
    NSUInteger x = t * (t + 3) / 2 - z;
    NSUInteger y = z - t * (t + 1) / 2;
    return [NSIndexPath indexPathForRow:y inSection:x];
}

Upvotes: 6

Paul
Paul

Reputation: 169

This is for a C# version, but should be almost identical in Objective-C:

http://sachiniscool.blogspot.com/2011/06/cantor-pairing-function-and-reversal.html

int CantorPair(short x, short y)
{
    return ((x + y) * (x + y + 1)) / 2 + y;
}

and to reverse the pairing

short[] Reverse(int z)
{
    short[] pair = new short[2];
    int t = (int)Math.Floor((-1D + Math.Sqrt(1D + 8 * z))/2D);
    int x = t * (t + 3) / 2 - z;
    int y = z - t * (t + 1) / 2;
    pair[0] = (short)x;
    pair[1] = (short)y;
    return pair;
}

Upvotes: 2

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