cog/Playlist/Shuffle.m

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//
// Shuffle.m
// Cog
//
// Created by Vincent Spader on 1/14/06.
// Copyright 2006 Vincent Spader. All rights reserved.
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//
#import "Shuffle.h"
@implementation Shuffle
int sum(int n)
{
return (n*n+n)/2;
}
int reverse_sum(int n)
{
return (int)(ceil((-1.0 + sqrt(1.0 + 8.0*n))/2.0));
}
int randint(int low, int high)
{
return (random()%high)+low;
}
+ (NSMutableArray *)shuffleList:(NSArray *)l
{
srandom(time(NULL));
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NSMutableArray *a = [l mutableCopy];
NSMutableArray *b = [[NSMutableArray alloc] init];
while([a count] > 0)
{
int t, r, p;
t = sum([a count]);
r = randint(1, t);
p = reverse_sum(r) - 1;
printf("%i, %i, %i, %i\n", [a count], t, r, p);
[b insertObject:[a objectAtIndex:p] atIndex:0];
[a removeObjectAtIndex:p];
}
[a release];
return [b autorelease];
}
@end