如何在Objective-C中反轉NSArray？

我須要扭轉個人NSArray 。

舉個例子：

[1,2,3,4,5]必須成爲： [5,4,3,2,1]

實現這一目標的最佳方法是什麼？

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#1樓

試試這個：

for (int i = 0; i < [arr count]; i++)
{
    NSString *str1 = [arr objectAtIndex:[arr count]-1];
    [arr insertObject:str1 atIndex:i];
    [arr removeObjectAtIndex:[arr count]-1];
}

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#2樓

至於我，您是否考慮過首先如何填充陣列？ 我正在將MANY對象添加到數組中，並決定在開頭插入每一個對象，將任何現有對象向上推一個。 在這種狀況下，須要一個可變數組。

NSMutableArray *myMutableArray = [[NSMutableArray alloc] initWithCapacity:1];
[myMutableArray insertObject:aNewObject atIndex:0];

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#3樓

若是你想作的只是反向迭代，試試這個：

// iterate backwards
nextIndex = (currentIndex == 0) ? [myArray count] - 1 : (currentIndex - 1) % [myArray count];

您能夠執行[myArrayCount]一次並將其保存到本地變量（我認爲它很昂貴），但我也猜想編譯器幾乎會對上面編寫的代碼作一樣的事情。

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#4樓

NSMutableArray *objMyObject = [NSMutableArray arrayWithArray:[self reverseArray:objArrayToBeReversed]];

// Function reverseArray 
-(NSArray *) reverseArray : (NSArray *) myArray {   
    return [[myArray reverseObjectEnumerator] allObjects];
}

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#5樓

一些基準

1. reverseObjectEnumerator allObjects

這是最快的方法：

NSArray *anArray = @[@"aa", @"ab", @"ac", @"ad", @"ae", @"af", @"ag",
        @"ah", @"ai", @"aj", @"ak", @"al", @"am", @"an", @"ao", @"ap", @"aq", @"ar", @"as", @"at",
        @"au", @"av", @"aw", @"ax", @"ay", @"az", @"ba", @"bb", @"bc", @"bd", @"bf", @"bg", @"bh",
        @"bi", @"bj", @"bk", @"bl", @"bm", @"bn", @"bo", @"bp", @"bq", @"br", @"bs", @"bt", @"bu",
        @"bv", @"bw", @"bx", @"by", @"bz", @"ca", @"cb", @"cc", @"cd", @"ce", @"cf", @"cg", @"ch",
        @"ci", @"cj", @"ck", @"cl", @"cm", @"cn", @"co", @"cp", @"cq", @"cr", @"cs", @"ct", @"cu",
        @"cv", @"cw", @"cx", @"cy", @"cz"];

NSDate *methodStart = [NSDate date];

NSArray *reversed = [[anArray reverseObjectEnumerator] allObjects];

NSDate *methodFinish = [NSDate date];
NSTimeInterval executionTime = [methodFinish timeIntervalSinceDate:methodStart];
NSLog(@"executionTime = %f", executionTime);

結果： executionTime = 0.000026

2.迭代reverseObjectEnumerator

這速度在1.5x到2.5x之間：

NSDate *methodStart = [NSDate date];
NSMutableArray *array = [NSMutableArray arrayWithCapacity:[anArray count]];
NSEnumerator *enumerator = [anArray reverseObjectEnumerator];
for (id element in enumerator) {
    [array addObject:element];
}
NSDate *methodFinish = [NSDate date];
NSTimeInterval executionTime = [methodFinish timeIntervalSinceDate:methodStart];
NSLog(@"executionTime = %f", executionTime);

結果： executionTime = 0.000071

3. sortedArrayUsingComparator

速度在30x到40x之間（這裏沒有驚喜）：

NSDate *methodStart = [NSDate date];
NSArray *reversed = [anArray sortedArrayUsingComparator: ^(id obj1, id obj2) {
    return [anArray indexOfObject:obj1] < [anArray indexOfObject:obj2] ? NSOrderedDescending : NSOrderedAscending;
}];

NSDate *methodFinish = [NSDate date];
NSTimeInterval executionTime = [methodFinish timeIntervalSinceDate:methodStart];
NSLog(@"executionTime = %f", executionTime);

結果： executionTime = 0.001100

因此[[anArray reverseObjectEnumerator] allObjects]在速度和輕鬆方面是明顯的贏家。