Question

Is there a class (function, method etc or any feature) like below feature?

example of conception)

A class that making all case combination.

    NSString *sourceString = [[NSString alloc] initWithString:@"ABC"];
    NSArray *sourceArray = [[NSArray alloc] initWithObjects:@"A", @"B", @"C"];

    someClass *someClass1 = [[someClass alloc] init];

    NSString *caseResultAsString = [someClass1 makeAllCaseCombinationToStr:sourceString pair:2];
    NSArray *caseResultAsArray = [someClass1 makeAllCaseCombinationToArray:sourceArray pair:2];

value of caseResultAsString is
“AA AB AC BA BB BC CA CB CC” (pair argument is 2)

value of caseResultAsArray is
{“AA”,
“AB”,
“AC”,
“BA”,
“BB”,
“BC”,
“CA”,
“CB”,
“CC”}

If input source and output result is any type or any way, it doesn’t matter.

I want to know if there is a class with feature of above conception.

Answer 1

Here’s a very simple NSSet category:

@interface NSSet(Permutations)

-(NSSet *) setWithPermuations:(int) n;

@end

@implementation NSSet(Permutations)

// data should be NULL the first time through
static void for_loop(int count, int levels, void (^block)(int *levels), int *data)
{
    int freeData = 0;
    if (!data)
    {
        data = malloc(sizeof(int) * levels);
        freeData = 1;
    }

    for (int i = 0; i < count; i++) {
        data[levels - 1] = i;

        if (levels)
            for_loop(count, levels - 1, block, data);
        else {
            if (block)
                block(data);
        }
    }

    if (freeData)
        free(data);
}

-(NSSet *) setWithPermuations:(int)n
{
    NSMutableArray *returnArray = [NSMutableArray array];
    NSArray *thisArray = [self allObjects];

    for_loop(thisArray.count, n, ^(int *levels) {
        NSMutableString *concat = [NSMutableString string];

        for (int i = 0; i < n; i++) {
            [concat appendFormat:@"%@", [thisArray objectAtIndex:levels[i]]];
        }

        [returnArray addObject:concat];

    }, NULL);

    return [NSSet setWithArray:returnArray];
}

@end

Obviously, the algorithm’s time is O((N^T) + O(N)), where N is the elements in the set and T is the number of objects per permeation. This could easily be changed to have a NSSet of NSArrays if you wanted, but This currently just uses a string.