ObjC Trie Insert and Find

TrieNode.m

// TrieNode
// TrieNodes hold a dictionary of child TrieNode objects keyed by their character.
// isValid == YES means that the word exists in the dictionary

@interface TrieNode : NSObject
@property (strong, nonatomic) NSMutableDictionary<NSString *, TrieNode *> *children;
@property (assign, nonatomic) BOOL isValid;
-(instancetype)init;
@end


@implementation TrieNode
+(instancetype)init {
    self = [super init];
    if (self) {
        _children = [[NSMutableDictionary alloc] init];
        _isValid = NO;
    }
    return self;
}
@end

- (void)insertWord:(NSString *)word intoTrie:(TrieNode *)trie {
    NSUInteger len = word.length;
    unichar buffer[len];
    [word getCharacters:buffer range:NSMakeRange(0, len)];

    TrieNode *current = trie;

    for (int i = 0; i < len; ++i) {
        BOOL trieContainsKey = [current.children objectForKey:@(buffer[i]).stringValue];
        if (!trieContainsKey) {
            TrieNode *newNode = [[TrieNode alloc] init];
            [current.children setValue:newNode forKey:@(buffer[i]).stringValue];
            current = newNode;
        } else {
            current = [current.children objectForKey:@(buffer[i]).stringValue];
        }
    }
    current.isValid = YES;
}

- (BOOL)containsWord:(NSString *)word trie:(TrieNode *)trie {
    NSUInteger len = word.length;
    unichar buffer[len];
    [word getCharacters:buffer range:NSMakeRange(0, len)];

    TrieNode* current = trie;
    for (int i = 0; i < len; ++i) {
        TrieNode* nextNode = [current.children objectForKey:@(buffer[i]).stringValue];
        current = nextNode;
    }
    return current.isValid;
}