Objective-c Priority Queue

Question

I've started using Objective-c for iOS programming. I switched over from Java, and I wanted to know if there were any existing libraries like the Java Collections Framework for Obj-c, more specifically a priority queue implementation. I've done some searches, but have been unable to come up with anything.

UPDATE: I found this, but would have no idea how to use it myself: http://www.ohloh.net/p/pqlib

Answer 1

I was unable to find an implementation of a priority queue, so I went ahead and made my own. I'm not sure how robust it is, but I hope it might point others in the right direction.

PriorityQueue.h

//
//  PriorityQueue.h
//

#import <Foundation/Foundation.h>
#import "comparable.h"

//Implements a priority queue. All objects in queue must implement the comparable protocol and must be all of the same type. The queue can be explicity typed at initialization, otherwise the type of the first object entered will be the type of the queue
@interface PriorityQueue : NSObject{
    NSMutableArray *queue;
    Class type;
}

- (id)init;
- (id)initWithObjects:(NSSet *)objects;
- (id)initWithCapacity:(int)capacity;
- (id)initWithCapacity:(int)capacity andType:(Class)oType; //Queue will reject objects not of that type

#pragma mark - Useful information
- (BOOL)isEmpty;
- (BOOL)contains:(id<comparable, NSObject>)object;
- (Class)typeOfAllowedObjects; //Returns the type of objects allowed to be stored in the queue
- (int) size;

#pragma mark - Mutation
- (void)clear;
- (BOOL)add:(id<comparable, NSObject>)object;
- (void)remove:(id<comparable, NSObject>)object;

#pragma mark - Getting things out
- (id)peek;
- (id)poll;
- (id)objectMatchingObject:(id<comparable, NSObject>)object;
- (NSArray *)toArray;

#pragma mark -
- (void)print;

@end

PriorityQueue.m

//
//  PriorityQueue.m
//

#import "PriorityQueue.h"

#define INITIAL_CAPACITY 50
@implementation PriorityQueue

#pragma mark - Initialization
- (id)init{
    return [self initWithCapacity:INITIAL_CAPACITY andType:nil];
}

- (id)initWithObjects:(NSSet *)objects{
    self = [self initWithCapacity:INITIAL_CAPACITY andType:nil];
    for (id<comparable, NSObject>object in objects){
        [self add:object];
    }
    return self;
}

- (id)initWithCapacity:(int)capacity{
    return [self initWithCapacity:capacity andType:nil];
}

- (id)initWithCapacity:(int)capacity andType:(Class)oType{
    self = [super init];
    if(self){
        queue = [[NSMutableArray alloc] init];
        type = oType;
    }
    return self;
}

#pragma mark - Useful information
- (BOOL)isEmpty{
    if(queue.count == 0){
        return YES;
    }
    else{ return NO;}
}

- (BOOL)contains:(id<comparable, NSObject>)object{
    //Search the array to see if the object is already there
    for(id<comparable> o in queue){
        if([o isEqual:object]){
            return YES;
        }
    }
    return NO;
}

- (Class)typeOfAllowedObjects{
    NSLog(@"Allowed Types: %@", type);
    return type;
}

- (int) size{
    return [queue count];
}

#pragma mark - Mutation
//Mutation
- (void)clear{
    [queue removeAllObjects];
}

//A "greater" object (compareTo returns 1) is at the end of the queue.
- (BOOL)add:(id<comparable, NSObject>)object{
    //Make sure the object's type is the same as the type of the queue
    if(type == nil){
//        NSLog(@"Type is nil");
        type = [object class];
    }
    if([object class] != type){
        NSLog(@"ERROR: Trying to add incorrect object");
        return NO;
    }

    if([queue count] == 0){
        [queue addObject:object];
        return YES;
    }
    for(int i = 0; i < [queue count]; i++){
        if([object compareTo:queue[i]] < 0){
            [queue insertObject:object atIndex:i];
            return YES;
        }
    }
    [queue addObject:object];
    return YES;
}

- (void)remove:(id<comparable, NSObject>)object{
    [queue removeObject:object];
}

#pragma mark - Getting things out
- (id)peek{
    return queue[0];
}

- (id)poll{
    //Get the object at the front
    id head = queue[0];

    //Remove and return that object
    [queue removeObject:head];
    return head;
}

- (id)objectMatchingObject:(id<comparable, NSObject>)object{
    //Search the array to see if the object is already there
    for(id<comparable> o in queue){
        if([o isEqual:object]){
            return o;
        }
    }
    return nil;
}

- (NSArray *)toArray{
    return [[NSArray alloc] initWithArray:queue];
}

#pragma mark -
- (NSString *)description{
    return [NSString stringWithFormat:@"PriorityQueue: %@ allows objects of type %@", queue, type];
}

- (void)print{
    NSLog(@"%@", [self description]);
}

@end

Comparable.h

//
//  comparable.h
//

#import <Foundation/Foundation.h>


//NOTE: Class must check to make sure it is the same class as whatever is passed in
@protocol comparable

- (int)compareTo:(id<comparable, NSObject>)object;
- (BOOL)isEqual:(id<comparable, NSObject>)object;

@end