两种快速打乱NSMutableArray的方法

1。利用交换

//  NSMutableArray_Shuffling.h

#if TARGET_OS_IPHONE
#import <UIKit/UIKit.h>
#else
#include <Cocoa/Cocoa.h>
#endif

// This category enhances NSMutableArray by providing
// methods to randomly shuffle the elements.
@interface NSMutableArray (Shuffling)
- (void)shuffle;
@end


//  NSMutableArray_Shuffling.m

#import "NSMutableArray_Shuffling.h"

@implementation NSMutableArray (Shuffling)

- (void)shuffle
{
    NSUInteger count = [self count];
    for (NSUInteger i = 0; i < count; ++i) {
        // Select a random element between i and end of array to swap with.
        int nElements = count - i;
        int n = (random() % nElements) + i;
        [self exchangeObjectAtIndex:i withObjectAtIndex:n];
    }
}

@end

2。利用排序

int randomSort(id obj1, id obj2, void *context ) {
        // returns random number -1 0 1
    return (random()%3 - 1);    
}

- (void)shuffle {
        // call custom sort function
    [puzzles sortUsingFunction:randomSort context:nil];

    // show in log how is our array sorted
        int i = 0;
    for (Puzzle * puzzle in puzzles) {
        NSLog(@" #%d has index %d", i, puzzle.index);
        i++;
    }
}
log output:
 #0 has index #6
 #1 has index #3
 #2 has index #9
 #3 has index #15
 #4 has index #8
 #5 has index #0
 #6 has index #1
 #7 has index #4
 #8 has index #7
 #9 has index #12
 #10 has index #14
 #11 has index #16
 #12 has index #17
 #13 has index #10
 #14 has index #11
 #15 has index #13
 #16 has index #5
 #17 has index #2

you may as well compare obj1 with obj2 and decide what you want to return possible values are:

NSOrderedAscending = -1
NSOrderedSame = 0
NSOrderedDescending = 1