Add queue and stack implemention to NSMutableArray class

NSMutableArray+QueueAndStack.h

#import <Foundation/Foundation.h>

@interface NSMutableArray (QueueAndStack)
-(id)queuePop;
-(void)queuePush:(id)obj;
-(id)stackPop;
-(void)stackPush:(id)obj;
@end

NSMutableArray+QueueAndStack.m

#import "NSMutableArray+QueueAndStack.h"

@implementation NSMutableArray (QueueAndStack)
// Queues are first-in-first-out, so we remove objects from the head
-(id)queuePop {
    if ([self count] == 0) {
        return nil;
    }
    
    id queueObject = [self objectAtIndex:0];
    
    [self removeObjectAtIndex:0];
    
    return queueObject;
}

// Add to the tail of the queue
-(void)queuePush:(id)anObject {
    [self addObject:anObject];
}

//Stacks are last-in-first-out.
-(id)stackPop {
    id lastObject = [self lastObject];
    
    if (lastObject)
        [self removeLastObject];
    
    return lastObject;
}

-(void)stackPush:(id)obj {
    [self addObject: obj];
}
@end