Deep copy cyclic graph

@interface GraphNode : NSObject
@property (nonatomic, copy) NSArray<GraphNode *> *neighbors;
@property (nonatomic, copy) NSString *name;
@end

@interface Graph : NSObject<NSCopying>
@property (nonatomic, copy) NSArray<GraphNode *> *nodes;
@end

@implementation GraphNode
- (instancetype)init {
    self = [super init];
    if(self) {
        _neighbors = [NSMutableArray new];
    }
    return self;
}
@end

@implementation Graph
- (instancetype)init {
    self = [super init];
    if(self) {
        _nodes = [NSMutableArray new];
    }
    return self;
}
- (id)copyWithZone:(NSZone *)zone {
    NSMutableArray<GraphNode *> *copiedNodes = [NSMutableArray new];
    NSMutableDictionary<NSString *, GraphNode *> *copies = [NSMutableDictionary new];
    for(GraphNode *node in self.nodes) {
        GraphNode *copied = [GraphNode new];
        copied.name = node.name;
        copied.neighbors = [node.neighbors copy];
        [copiedNodes addObject:copied];
        copies[node.name] = copied;
    }
    for(GraphNode *node in self.nodes) {
        NSMutableArray<GraphNode *> *copiedNeighbors = [NSMutableArray new];
        for(GraphNode *neighbor in node.neighbors) {
            [copiedNeighbors addObject:copies[neighbor.name]];
        }
        copies[node.name].neighbors = copiedNeighbors;
    }

    Graph *copy = [Graph new];
    copy.nodes = copiedNodes;
    return copy;
}
@end