关于C#:什么是洗牌NSMutableArray的最佳方式?

关于C#:什么是洗牌NSMutableArray的最佳方式?

What's the Best Way to Shuffle an NSMutableArray?

如果你有一个NSMutableArray,你如何随机地改变元素?

(我有自己的答案,这是张贴在下面,但我是新的可可,我有兴趣知道是否有更好的方法。)

更新:正如@mukesh所指出的,从iOS 10+和MacOS 10.12+开始,有一个-[NSMutableArray shuffledArray]方法可用于无序播放。请参阅https://developer.apple.com/documentation/foundation/nsarray/1640855-shuffedarray?语言=objc了解详细信息。(但请注意,这将创建一个新的数组,而不是将元素重新排列到位。)


我通过向nsmutablearray添加一个类别来解决这个问题。

编辑:删除了不必要的方法,感谢LADD的回答。

编辑:由于Gregory Goltsov的回答和Miho和Blahdiblah的评论,(arc4random() % nElements)改为arc4random_uniform(nElements)

编辑:循环改进,感谢Ron的评论

编辑:添加检查数组是否不为空,这要感谢Mahesh Agrawal的评论。

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//  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];
    if (count <= 1) return;
    for (NSUInteger i = 0; i < count - 1; ++i) {
        NSInteger remainingCount = count - i;
        NSInteger exchangeIndex = i + arc4random_uniform((u_int32_t )remainingCount);
        [self exchangeObjectAtIndex:i withObjectAtIndex:exchangeIndex];
    }
}

@end

你不需要swapobjectatindex方法。ExchangeObjectAtindex:WithObjectAtindex:已存在。


既然我还不能发表评论,我想我会给出一个完整的回应。我以多种方式修改了Kristopher Johnson对我的项目的实现(真的试图使其尽可能简洁),其中之一是arc4random_uniform(),因为它避免了模块偏差。

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// NSMutableArray+Shuffling.h
#import <Foundation/Foundation.h>

/** This category enhances NSMutableArray by providing methods to randomly
 * shuffle the elements using the Fisher-Yates algorithm.
 */

@interface NSMutableArray (Shuffling)
- (void)shuffle;
@end

// NSMutableArray+Shuffling.m
#import"NSMutableArray+Shuffling.h"

@implementation NSMutableArray (Shuffling)

- (void)shuffle
{
    NSUInteger count = [self count];
    for (uint i = 0; i < count - 1; ++i)
    {
        // Select a random element between i and end of array to swap with.
        int nElements = count - i;
        int n = arc4random_uniform(nElements) + i;
        [self exchangeObjectAtIndex:i withObjectAtIndex:n];
    }
}

@end

从iOS 10可以使用新的shuffledAPI:

https://developer.apple.com/reference/foundation/nsarray/1640855-无序播放

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let shuffledArray = array.shuffled()


一个稍微改进和简洁的解决方案(与最重要的答案相比)。

该算法与文献中描述的"Fisher-Yates shuffle"相同。

在目标C中:

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@implementation NSMutableArray (Shuffle)
// Fisher-Yates shuffle
- (void)shuffle
{
    for (NSUInteger i = self.count; i > 1; i--)
        [self exchangeObjectAtIndex:i - 1 withObjectAtIndex:arc4random_uniform((u_int32_t)i)];
}
@end

在Swift 3.2和4.x中:

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extension Array {
    /// Fisher-Yates shuffle
    mutating func shuffle() {
        for i in stride(from: count - 1, to: 0, by: -1) {
            swapAt(i, Int(arc4random_uniform(UInt32(i + 1))))
        }
    }
}

在Swift 3.0和3.1中:

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extension Array {
    /// Fisher-Yates shuffle
    mutating func shuffle() {
        for i in stride(from: count - 1, to: 0, by: -1) {
            let j = Int(arc4random_uniform(UInt32(i + 1)))
            (self[i], self[j]) = (self[j], self[i])
        }
    }
}

注:使用GameplayKit可以从IOS10获得更简洁的swift解决方案。

注:还提供了一种不稳定洗牌的算法(如果计数>1,则强制更改所有位置)。


这是最简单和最快的方法来洗牌NSarray或NSmutableArrays(对象拼图是一个非可变数组,它包含拼图对象。我已添加到指示数组中初始位置的益智对象变量索引)

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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++;
    }
}

日志输出:

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 #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

您也可以将obj1与obj2进行比较,并决定要返回的内容可能的值是:

  • nsOrderedAscending=-1
  • nsOrderedName=0
  • nsOrderedDescending=1


从iOS 10,您可以使用游戏工具包中的nsarray shuffled()。以下是Swift 3中数组的助手:

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import GameplayKit

extension Array {
    @available(iOS 10.0, macOS 10.12, tvOS 10.0, *)
    func shuffled() -> [Element] {
        return (self as NSArray).shuffled() as! [Element]
    }
    @available(iOS 10.0, macOS 10.12, tvOS 10.0, *)
    mutating func shuffle() {
        replaceSubrange(0..<count, with: shuffled())
    }
}


有一个很好的流行库,它有这个方法作为它的一部分,在GitHub中称为sstoolkit。文件nsmutablerray+sstoolkitadditions.h包含shuffle方法。你也可以用它。其中,似乎有很多有用的东西。

这个图书馆的主页在这里。

如果使用此代码,则代码如下:

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#import <SSCategories.h>
NSMutableArray *tableData = [NSMutableArray arrayWithArray:[temp shuffledArray]];

这个图书馆也有一个豆荚(见椰子)


如果元素有重复。

例如阵列:A A A B或B B A A

唯一的解决办法是:A B A B A

sequenceSelected是一个NSmutableArray,它存储类obj的元素,这些元素是指向某个序列的指针。

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- (void)shuffleSequenceSelected {
    [sequenceSelected shuffle];
    [self shuffleSequenceSelectedLoop];
}

- (void)shuffleSequenceSelectedLoop {
    NSUInteger count = sequenceSelected.count;
    for (NSUInteger i = 1; i < count-1; i++) {
        // Select a random element between i and end of array to swap with.
        NSInteger nElements = count - i;
        NSInteger n;
        if (i < count-2) { // i is between second  and second last element
            obj *A = [sequenceSelected objectAtIndex:i-1];
            obj *B = [sequenceSelected objectAtIndex:i];
            if (A == B) { // shuffle if current & previous same
                do {
                    n = arc4random_uniform(nElements) + i;
                    B = [sequenceSelected objectAtIndex:n];
                } while (A == B);
                [sequenceSelected exchangeObjectAtIndex:i withObjectAtIndex:n];
            }
        } else if (i == count-2) { // second last value to be shuffled with last value
            obj *A = [sequenceSelected objectAtIndex:i-1];// previous value
            obj *B = [sequenceSelected objectAtIndex:i]; // second last value
            obj *C = [sequenceSelected lastObject]; // last value
            if (A == B && B == C) {
                //reshufle
                sequenceSelected = [[[sequenceSelected reverseObjectEnumerator] allObjects] mutableCopy];
                [self shuffleSequenceSelectedLoop];
                return;
            }
            if (A == B) {
                if (B != C) {
                    [sequenceSelected exchangeObjectAtIndex:i withObjectAtIndex:count-1];
                } else {
                    // reshuffle
                    sequenceSelected = [[[sequenceSelected reverseObjectEnumerator] allObjects] mutableCopy];
                    [self shuffleSequenceSelectedLoop];
                    return;
                }
            }
        }
    }
}


克里斯托弗·约翰逊的回答很好,但并不是完全随机的。

给定一个由2个元素组成的数组,此函数总是返回逆数组,因为生成的是剩余索引的随机范围。更精确的shuffle()函数如下

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- (void)shuffle
{
   NSUInteger count = [self count];
   for (NSUInteger i = 0; i < count; ++i) {
       NSInteger exchangeIndex = arc4random_uniform(count);
       if (i != exchangeIndex) {
            [self exchangeObjectAtIndex:i withObjectAtIndex:exchangeIndex];
       }
   }
}

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NSUInteger randomIndex = arc4random() % [theArray count];


编辑:这不正确。出于参考目的,我没有删除这篇文章。请参阅有关此方法不正确的原因的注释。

此处为简单代码:

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- (NSArray *)shuffledArray:(NSArray *)array
{
    return [array sortedArrayUsingComparator:^NSComparisonResult(id obj1, id obj2) {
        if (arc4random() % 2) {
            return NSOrderedAscending;
        } else {
            return NSOrderedDescending;
        }
    }];
}


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