iOS 實現(xiàn)一個棧
蘋果的Cocoa并沒有暴露系統(tǒng)的棧結(jié)構(gòu) ，這里根據(jù)棧的特點(diǎn)，使用數(shù)組實現(xiàn)了一個簡單的棧。

MyStack.h

@interface MyStack : NSObject

- (void)push:(id)obj;

- (id)pop;

- (id)peek;

@end

MyStack.m

#import "MyStack.h"

// 定義棧的容量
#define kStackSize  10

@interface MyStack ()

@property (nonatomic, strong) NSMutableArray *list;

@property (nonatomic, assign) NSInteger size; // the number of stack elements

@end

@implementation MyStack

- (instancetype)init
{
    self = [super init];
    if (self) {
        
        self.list = [NSMutableArray arrayWithCapacity:kStackSize];
        self.size = 0;
        
    }
    return self;
}

- (void)push:(id)obj
{
    if ([self isFull] || !obj) return;

    [self.list addObject:obj];
    self.size++;
}

- (id)pop
{
    if ([self isEmpty]) return nil;
    
    id obj = [self.list objectAtIndex:self.size -1];
    [self.list removeObjectAtIndex:self.size - 1];
    self.size--;
    return obj;
}

- (id)peek
{
    if ([self isEmpty]) return nil;
    
    id obj = [self.list objectAtIndex:self.size -1];
    return obj;
}

- (BOOL)isEmpty
{
    return self.size == 0;
}

- (BOOL)isFull
{
    return self.size == kStackSize;
}
@end

線程安全的 MyStack.m

#import "MyStack.h"

#define kStackSize  10

@interface MyStack ()

@property (nonatomic, strong) NSMutableArray *list;

@property (nonatomic, assign) NSInteger size; // the number of stack elements

@property (nonatomic, strong) dispatch_semaphore_t semaphore;  // 信號量  鎖

@end


@implementation MyStack

- (instancetype)init
{
    self = [super init];
    if (self) {
        
        self.list = [NSMutableArray arrayWithCapacity:kStackSize];
        self.size = 0;
        self.semaphore = dispatch_semaphore_create(1);
        
    }
    return self;
}

- (void)push:(id)obj
{
    if ([self isFull] || !obj) return;
    
    dispatch_semaphore_wait(self.semaphore, DISPATCH_TIME_FOREVER);
    [self.list addObject:obj];
    self.size++;
    dispatch_semaphore_signal(self.semaphore);
}

- (id)pop
{
    if ([self isEmpty]) return nil;
    
    dispatch_semaphore_wait(self.semaphore, DISPATCH_TIME_FOREVER);
    id obj = [self.list objectAtIndex:self.size -1];
    [self.list removeObjectAtIndex:self.size - 1];
    self.size--;
    dispatch_semaphore_signal(self.semaphore);
    return obj;
}

- (id)peek
{
    if ([self isEmpty]) return nil;
    
    id obj = [self.list objectAtIndex:self.size -1];
    return obj;
}

- (BOOL)isEmpty
{
    return self.size == 0;
}

- (BOOL)isFull
{
    return self.size == kStackSize;
}

@end

測試代碼

MyStack *stack = [[MyStack alloc] init];

[stack push:@(1)];
[stack push:@(2)];
[stack push:@(3)];

NSLog(@"%@", [stack peek]);

NSLog(@"%@", [stack pop]);
NSLog(@"%@", [stack pop]);
NSLog(@"%@", [stack pop]);
NSLog(@"%@", [stack pop]);


輸出結(jié)果：
2022-01-02 21:52:04.782525+0800 MyStack[15061:347654] 3
2022-01-02 21:52:04.783088+0800 MyStack[15061:347654] 3
2022-01-02 21:52:04.783163+0800 MyStack[15061:347654] 2
2022-01-02 21:52:04.783226+0800 MyStack[15061:347654] 1
2022-01-02 21:52:04.783247+0800 MyStack[15061:347654] (null)