我正在尝试使用objective-c块实现二进制搜索。我正在使用函数indexOfObject:inSortedRange:options:usingComparator:
。这是一个例子。
// A pile of data.
NSUInteger amount = 900000;
// A number to search for.
NSNumber* number = [NSNumber numberWithInt:724242];
// Create some array.
NSMutableArray* array = [NSMutableArray arrayWithCapacity:amount];
for (NSUInteger i = 0; i < amount; ++i) {;
[array addObject:[NSNumber numberWithUnsignedInteger:i]];
}
NSTimeInterval start = [NSDate timeIntervalSinceReferenceDate];
// Run binary search.
int index1 = [array indexOfObject:number
inSortedRange:NSMakeRange(0, [array count])
options:NSBinarySearchingFirstEqual
usingComparator:^(id lhs, id rhs) {
if ([lhs intValue] < [rhs intValue]) {
return (NSComparisonResult)NSOrderedAscending;
} else if([lhs intValue] > [rhs intValue]) {
return (NSComparisonResult)NSOrderedDescending;
}
return (NSComparisonResult)NSOrderedSame;
}];
NSTimeInterval stop1 = [NSDate timeIntervalSinceReferenceDate];
NSLog(@"Binary: Found index position: %d in %f seconds.", index1, stop1 - start);
// Run normal search.
int index2 = [array indexOfObject:number];
NSTimeInterval stop2 = [NSDate timeIntervalSinceReferenceDate];
NSLog(@"Normal: Found index position: %d in %f seconds.", index2, stop2 - start);
我想知道如何使用具有上述功能的外部定义的objective-c块。这是两个比较函数。
NSComparisonResult compareNSNumber(id lhs, id rhs) {
return [lhs intValue] < [rhs intValue] ? NSOrderedAscending : [lhs intValue] > [rhs intValue] ? NSOrderedDescending : NSOrderedSame;
}
NSComparisonResult compareInt(int lhs, int rhs) {
return lhs < rhs ? NSOrderedAscending : lhs > rhs ? NSOrderedDescending : NSOrderedSame;
}
这些是参考以下声明而写的,可以在NSObjCRuntime.h
。
enum _NSComparisonResult {NSOrderedAscending = -1, NSOrderedSame, NSOrderedDescending};
typedef NSInteger NSComparisonResult;
typedef NSComparisonResult (^NSComparator)(id obj1, id obj2);
答案 0 :(得分:21)
您可以将块定义为全局变量,以获得与函数类似的效果。
NSComparisonResult (^globalBlock)(id,id) = ^(id lhs, id rhs) {
if([lhs intValue] < [rhs intValue]) {
return (NSComparisonResult)NSOrderedAscending;
} else if([lhs intValue] > [rhs intValue]) {
return (NSComparisonResult)NSOrderedDescending;
}
return (NSComparisonResult)NSOrderedSame;
};
然后,在进行比较的方法中:
int index1 = [array indexOfObject:number
inSortedRange:NSMakeRange(0, [array count])
options:NSBinarySearchingFirstEqual
usingComparator:globalBlock];
将块放在标题中,供外部使用:
NSComparisonResult (^globalBlock)(id,id);
答案 1 :(得分:2)
我知道这已经过时了,但我只是碰到了它并且我一直在尝试使用我的块foo,所以这里......
我创建了一个将NSComparator作为块返回的方法。它看起来像这样:
-(NSComparisonResult (^) (id lhs, id rhs))compareNSNumber{
return [[^(id lhs, id rhs)
{
return [lhs intValue] < [rhs intValue] ? (NSComparisonResult)NSOrderedAscending : [lhs intValue] > [rhs intValue] ? (NSComparisonResult)NSOrderedDescending : (NSComparisonResult)NSOrderedSame;
} copy ] autorelease];
}
然后,我可以通过将二进制搜索执行更改为:
来运行示例代码// Run binary search.
int index1 = [array indexOfObject:number
inSortedRange:NSMakeRange(0, [array count])
options:NSBinarySearchingFirstEqual
usingComparator:[self compareNSNumber]];
NSTimeInterval stop1 = [NSDate timeIntervalSinceReferenceDate];
NSLog(@"Binary: Found index position: %d in %f seconds.", index1, stop1 - start);
我在方法调用中使用块定义获得了与原始实现非常相似的输出。