优先级队列

可以利用二叉堆来实现优先级队列，比如我们用大顶堆，堆顶为我们的最大元素，可以理解为优先级最高的元素，我们优先级队列也是优先级最高的先出对，所以每次从大顶堆取出一个元素，那么这个元素就是优先级最高的，然后相当于最大堆删除了一个元素，然后删除堆顶元素之后，这个堆依然为最大堆，下次再取也是优先级最高的。

代码

//
//  SCXPriorityQueue.m
//  TestArithmetic
//
//  Created by 孙承秀 on 2020/7/7.
//  Copyright © 2020 孙承秀. All rights reserved.
//

#import "SCXPriorityQueue.h"
#import "SCXBinaryHeap.h"
@interface SCXPriorityQueue()<SCXBinaryHeapDelegate>
@property (nonatomic , strong) SCXBinaryHeap *heap;
@property (nonatomic , weak) id<SCXPriorityQueueDelegate> delegate;
@end
@implementation SCXPriorityQueue
-(instancetype)initWithDelegate:(id)delegate{
    if (self = [super init]) {
        self.delegate = delegate;
        self.heap = [[SCXBinaryHeap alloc] initWithDelegate:self];
    }
    return self;;
}
-(NSInteger)size{
    return self.heap.size;
}
-(BOOL)isEmpty{
    return self.heap.isEmpty;
}
-(void)clear{
    [self.heap clear];
}
- (id)deQueue{
    return [self.heap removeTopObject];
}
- (void)enQueue:(id)obj{
    [self.heap add:obj];
}
-(id)front{
    return [self.heap getTopObject];;
}
-(BOOL)compareA:(id)valueA valueB:(id)valueB{
    if (self.delegate && [self.delegate respondsToSelector:@selector(compareA:valueB:)]) {
        return [self.delegate compareA:valueA valueB:valueB];
    }
    return YES;
}
-(NSString *)description{
    return self.heap.description;
}
@end

堆参考这篇文章