- (int)func0:(int)i {
    // do anything
    return [self func1:i];
}

- (int)func0:(int)i {
    // do anything
    if (i == 0) {
    	return [self func2:i];
    } else {
    	return [self func1:i];
    }
}

- (int)func0:(int)i {
    // do anything
    return [self func1:i] + 1;
}

- (int)func0:(int)i {
    // do anything
    int value = [self func1:i]
    return value;
}

- (int)func0:(int)i {
    // do anything
    return [self func0:i];
}

- (int)factorial0:(int)n {
    if (n < 1) return 0;
    if (n == 1) return 1;
    return n * [self factorial0:n - 1];
}

- (int)factorial1:(int)n {
    if (n < 1) return 0;
    return [self factorial1:n total:1];
}

- (int)factorial1:(int)n total:(int)total {
    if (n == 1) return total;
    return [self factorial1:n - 1 total:total * n];
}

// Person
@interface Person : NSObject
+ (instancetype)personWithType:(PersonType)personType;
- (void)doWork;
@end

@implementation Person
+ (instancetype)personWithType:(PersonType)personType {
    switch (personType) {
        case PersonTypeA:
            return [PersonA new];
            break;
        case PersonTypeB:
            return [PersonB new];
            break;
        case PersonTypeC:
            return [PersonC new];
            break;
    }
}

- (void)doWork {
    //SubClasses implement this
}
@end

//
// Subclass PersonA
@interface PersonA : Person

@end

@implementation PersonA

- (void)doWork {
    NSLog(@"do PersonA Work");
}

//
// Subclass PersonB
@interface PersonB : Person

@end

@implementation PersonB

- (void)doWork {
    NSLog(@"do PersonB Work");
}

//
// Subclass PersonC
@interface PersonC : Person

@end

@implementation PersonC

- (void)doWork {
    NSLog(@"do PersonC Work");
}

@end

Person *personA = [Person personWithType:PersonTypeA];
Person *personB = [Person personWithType:PersonTypeB];
Person *personC = [Person personWithType:PersonTypeC];

NSLog(@"%@",[personA class]);
NSLog(@"%@",[personB class]);
NSLog(@"%@",[personC class]);

[personA doWork];
[personB doWork];
[personC doWork];

// 输出
// PersonA
// PersonB
// PersonC
// do PersonA Work
// do PersonB Work
// do PersonC Work

/**
 * Policies related to associative references.
 * These are options to objc_setAssociatedObject()
 */
typedef OBJC_ENUM(uintptr_t, objc_AssociationPolicy) {
    OBJC_ASSOCIATION_ASSIGN = 0,           /**< Specifies a weak reference to the associated object. */
    OBJC_ASSOCIATION_RETAIN_NONATOMIC = 1, /**< Specifies a strong reference to the associated object. 
                                            *   The association is not made atomically. */
    OBJC_ASSOCIATION_COPY_NONATOMIC = 3,   /**< Specifies that the associated object is copied. 
                                            *   The association is not made atomically. */
    OBJC_ASSOCIATION_RETAIN = 01401,       /**< Specifies a strong reference to the associated object.
                                            *   The association is made atomically. */
    OBJC_ASSOCIATION_COPY = 01403          /**< Specifies that the associated object is copied.
                                            *   The association is made atomically. */
};

// 设置关联对象
void objc_setAssociatedObject(id _Nonnull object, const void * _Nonnull key,id _Nullable value, objc_AssociationPolicy policy);
// 获取关联对象
id objc_getAssociatedObject(id _Nonnull object, const void * _Nonnull key);                         
// 移除关联对象
void objc_removeAssociatedObjects(id _Nonnull object)   

- (void)showAlert {
	UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"title" message:@"message" delegate:self cancelButtonTitle:@"Cancel" otherButtonTitles:@"Confirm", nil];
	[alertView show];
}

- (void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex {
    if (buttonIndex == 0) {
        
    } else if (buttonIndex == 1) {
        
    }
}

#import <objc/runtime.h>

static const void *kAlertKey = @"kAlertKey";
- (void)showAlert {
	UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"title" message:@"message" delegate:self cancelButtonTitle:@"Cancel" otherButtonTitles:@"confirm", nil];
	
	void (^block)(NSInteger) = ^(NSInteger buttonIndex) {
		if (buttonIndex == 0) {
            
		} else if (buttonIndex == 1) {
            
		}
	};
	objc_setAssociatedObject(alertView, kAlertKey, block, OBJC_ASSOCIATION_COPY);
	[alertView show];
}

- (void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex {
    void (^block)(NSInteger) = objc_getAssociatedObject(alertView, kAlertKey);
    block(buttonIndex);
}

id returnValue = [someObject msgName:parameter];

id returnValue = objc_msgSend(someObject, @selector(msgName:), parameter);

@implementation
@synthesize firstName = _myFirstName;
@dynamic firstName;
@end

// NSString
- (BOOL)isEqualToString:(NSString *)aString;

// NSData
- (BOOL)isEqualToData:(NSData *)other;

// NSDictionary
- (BOOL)isEqualToDictionary:(NSDictionary<KeyType, ObjectType> *)otherDictionary;

- (BOOL)isEqual:(id)object;  
@property (readonly) NSUInteger hash;

@interface Person()
@property (nonatomic, copy) NSString *email;
@end

- (BOOL)isEqualToPerson:(Person *)otherPerson {
    if (nil == otherPerson) return NO;
    if (self == otherPerson) return YES;
    
    if ([_email isEqualToString:otherPerson.email]) return YES;
    
    return NO;
}

- (BOOL)isEqual:(id)object {
    if ([self class] != [object class]) return NO;
    
    [self isEqualToPerson:object];
    
    return NO;
}

// 如果两个对象相等，则其哈希码一定相同。反之，如果哈希码相同，这两个对象不一定相同。
// 考虑到性能问题，hash 方法要保证高效率
- (NSUInteger)hash {
	// 此处逻辑可以自定义
    return [_email hash];
}

// NSArray
- (BOOL)containsObject:(ObjectType)anObject;
// NSSet
- (BOOL)containsObject:(ObjectType)anObject;

NSMutableArray *array = [NSMutableArray array];
Person *aPerson = nil;
for (int i = 0; i < 5; i++) {
	Person *p = [[Person alloc] initWithEmail:[NSString stringWithFormat:@"%zd",i]];
	[array addObject:p];
	aPerson = p;
}
if ([array containsObject:aPerson]) {
	NSLog(@"array has 'aPerson'");
}

NSMutableSet *sets = [NSMutableSet set];
Person *aPerson = nil;
for (int i = 0; i < 5; i++) {
	Person *p = [[Person alloc] initWithEmail:[NSString stringWithFormat:@"%zd",i]];
	[sets addObject:p];
	aPerson = p;
}
if ([sets containsObject:aPerson]) {
	NSLog(@"array has 'aPerson'");
}

NSString *string0 = [[NSString alloc] initWithString:@"123"];
NSString *string1 = @"123";
    
NSNumber *number0 = [NSNumber numberWithInt:1];
NSNumber *number1 = @1;
    
NSArray *array0 = [NSArray arrayWithObjects:@"cat", @"dog", @"fish", nil];
NSString *cat0 = [array0 objectAtIndex:0];
NSArray *array1 = @[@"cat", @"dog", @"fish"];
NSString *cat1 = array1[0];
    
NSDictionary *dictionary0 = [NSDictionary dictionaryWithObjectsAndKeys:@"key0", @"value0", @"key1", @"value1", nil];
NSString *value0 = [dictionary0 objectForKey:@"key0"];
	
NSDictionary *dictionary1 = @{@"key0":@"value0", @"key1":@"value1"};
NSString *value1 = dictionary1[@"key1"];

#define kAnimationDuration 0.1
static const NSTimeInterval kAnimationDuration = 0.1;
static const float kAnimationDuration = 0.1;

// .h文件 声明一个变量
extern NSString *const VCHLoginNotification;
// .m文件 定义一个变量
NSString *const VCHLoginNotification = @"kLoginNotification";

float const valueFloat0 = 0.1; //[1]
const float valueFloat1 = 0.1; //[2]
NSString const * string0 = @"abc"; //[3]
NSString * const string1 = @"abc"; //[4]
const NSString * string2 = @"abc"; //[5]
const NSString * const string3 = @"abc"; //[6]
const NSString const * string4 = @"abc"; //[7]

// 状态、状态码
typedef NS_ENUM(NSInteger, UIViewAnimationTransition) {
    UIViewAnimationTransitionNone,
    UIViewAnimationTransitionFlipFromLeft,
    UIViewAnimationTransitionFlipFromRight,
    UIViewAnimationTransitionCurlUp,
    UIViewAnimationTransitionCurlDown,
};

// 可组合选项
typedef NS_OPTIONS(NSUInteger, UIViewAutoresizing) {
    UIViewAutoresizingNone                 = 0,
    UIViewAutoresizingFlexibleLeftMargin   = 1 << 0,
    UIViewAutoresizingFlexibleWidth        = 1 << 1,
    UIViewAutoresizingFlexibleRightMargin  = 1 << 2,
    UIViewAutoresizingFlexibleTopMargin    = 1 << 3,
    UIViewAutoresizingFlexibleHeight       = 1 << 4,
    UIViewAutoresizingFlexibleBottomMargin = 1 << 5
};

NSString *string = (NSString *)[[NSDate alloc] init];
//调用 NSString 的方法，编译通过
[string stringByAppendingString:@"abc"];
//调用 NSDate 的方法，编译不通过
//提示：No visible @interface for 'NSString' declares the selector 'isEqualToDate:'
[string isEqualToDate:[NSDate date]];

NSString *string = (NSString *)[[NSDate alloc] init];
//编译通过，运行崩溃
[string performSelector:@selector(stringByAppendingString:) withObject:@"abc" afterDelay:0];
//编译通过，运行通过
[string performSelector:@selector(isEqualToDate:) withObject:[NSDate date] afterDelay:0];

// Person
+ (void)initialize {
    NSLog(@"Person initialize.......");
}

// Person (Special)
+ (void)initialize {
    NSLog(@"Person (Special) initialize.......");
}

// Person (Special1)
+ (void)initialize {
    NSLog(@"Person (Special1) initialize.......");
}

+ (void)initialize {
    if (self == [Person self]) {
        NSLog(@"本类发来的 initialize 消息。%@ - %@",self,[Person self]);
    } else {
        NSLog(@"子类发来的 initialize 消息。%@ - %@",self,[Person self]);
    }
}

- (void)fineTwoNumberWithArray0:(int *)nums count:(int)count target:(int)target {
    int leftNum,rightNum;
    
    for (int i = 0; i < count - 1; i++) {
        leftNum = nums[i];
        for (int j = i + 1; j < count; j++) {
            rightNum = nums[j];
            if ((rightNum + leftNum) == target) {
                NSLog(@"%d + %d = %d",leftNum, rightNum, target);
            }
        }
    }
}

- (void)fineTwoNumberWithArray1:(int *)nums count:(int)count target:(int)target {
    int left = 0;
    int right = count - 1;
    int sum = 0;
    while(left <= right) {
        sum = nums[left] + nums[right];
        if (sum < target) {
            left += 1;
        } else if (sum > target) {
            right -= 1;
        } else {
            NSLog(@"%d + %d = %d",nums[left], nums[right], target);
            left += 1;
            right -= 1;
        }
    }
}

- (void)aFunction0:(int)n {
    NSLog(@"%zd",n); // 执行 1 次
}

- (void)aFunction1:(int)n {
    for (int i = 0; i < n; i++) { // n + 1 次
        NSLog(@"%zd",i); // n 次
    }
}

- (void)aFunction2:(int)n {
    for (int i = 0; i < n; i++) { // n + 1
        for (int j = 0; j < n; j++) { // n + 1
            NSLog(@"%zd",i); // n
        }
    }
}

- (int)aFunction3:(int *)nums count:(int)count target:(int)target {
    int left = 0;
    int right = count - 1;
    int mid = 0;
    while(left <= right) {
        mid = (left + right) >> 1;
        if (nums[mid] < target) {
            left = mid + 1;
        } else if (nums[mid] > target) {
            right = mid - 1;
        } else {
            return mid;
        }
    }
    return -1;
}

// 快速排序
- (void)quickSort:(int *)nums count:(int)count {
    int start = 0;
    int end = count - 1;
    int value = nums[start];
    
    if (count < 1) return;
    
    while (start < end) {
        //从数组右边往左查找一个小于value的元素
        while (start < end) {
            if (nums[end] < value) {
                nums[start] = nums[end];
                start++;
                break;
            } else {
                end--;
            }
        }
        //从数组左边往右查找一个大于value的元素
        while (start < end) {
            if (nums[start] > value) {
                nums[end] = nums[start];
                end--;
                break;
            } else {
                start++;
            }
        }
    }
    nums[start] = value;
    
    [self quickSort:nums count:start];
    [self quickSort:nums + start + 1 count:count - start - 1];
}