adds the capacity queue

DKQueue.m

@@ -18,6 +18,8 @@ -(id)init
     return self;
 }
 
+
+
 -(id)dequeue 
 {
     if ([array count] > 0) {

DWCapacityQueue.h

@@ -0,0 +1,22 @@
+//
+//  DWCapacityQueue.h
+//  drawme
+//
+//  Created by WuJieson on 16/7/22.
+//  Copyright © 2016年 Ge. All rights reserved.
+//
+
+#import <Foundation/Foundation.h>
+#import "DKQueue.h"
+
+@interface DWCapacityQueue : DKQueue
+
+@property (nonatomic, assign) NSUInteger capacity;
+
+-(instancetype)initWithCapacity:(NSInteger)numItems;
+
+// Remove all elements
+-(void)enqueueElementsFromArray:(NSArray*)arr;
+-(void)enqueueElementsFromQueue:(DKQueue*)queue;
+
+@end

DWCapacityQueue.m

@@ -0,0 +1,47 @@
+//
+//  DWCapacityQueue.m
+//  drawme
+//
+//  Created by WuJieson on 16/7/22.
+//  Copyright © 2016年 Ge. All rights reserved.
+//
+
+#import "DWCapacityQueue.h"
+
+@implementation DWCapacityQueue
+
+-(instancetype)initWithCapacity:(NSInteger)numItems
+{
+    self = [super init];
+    if (self) {
+        _capacity = numItems;
+        array = [NSMutableArray arrayWithCapacity:numItems];
+    }
+    return self;
+}
+
+-(void)enqueue:(id)element
+{
+    if ([array count] == _capacity) {
+        [self dequeue];
+    }
+    [array addObject:element];
+}
+
+-(void)enqueueElementsFromArray:(NSArray*)arr
+{
+    [array addObjectsFromArray:arr];
+    while ([array count] > _capacity) {
+        [self dequeue];
+    }
+}
+
+-(void)enqueueElementsFromQueue:(DKQueue*)queue
+{
+    while (![queue isEmpty]) {
+        [self enqueue:[queue dequeue]];
+    }
+}
+
+
+@end