Question

I am looking for the most efficient way to match an NSString against about 200,000 other strings in the minimum amount of time. Basically I need to check, every once in a while, whether or not a word that is inputted is part of the English language.

What are the ways I could do this? I’ve heard about hashtables– is that the best way?

---

Here is the code I settled on:

EDIT:
benchmarks for dictionary initialization to memory:

NSDate *start = [NSDate date];

NSLog(@"initWords");

//temporary 
NSString *_filePath = [[NSBundle mainBundle] pathForResource:kFILE_NAME_FOR_DICTIONARY ofType:@"txt"];

NSLog(@"%@",_filePath);

NSString *_fileContents = [[NSString alloc] init];
NSData *_binary = [NSData dataWithContentsOfFile:_filePath];  

if (_binary) {  
    _fileContents = [[NSString alloc] initWithData:_binary encoding:NSUTF8StringEncoding];
}  else {

    NSLog(@"file parse error: did you forget to add the file? Please add file to:\n\n\n\n%@\n\n\n\n",[[NSBundle mainBundle] resourcePath]);
}

NSArray *_wordList = [_fileContents componentsSeparatedByString:kNEW_LINE_CHAR];

englishDictionary = [[NSMutableSet alloc] init];
[englishDictionary addObjectsFromArray:_wordList];

NSLog(@"Word count:\t%d",englishDictionary.count);
NSLog(@"Time to init dictionary:\t%f",[start timeIntervalSinceNow]*-1.);

iphone 5: 1.089725 (seconds)

ipad 1: 3.082753

iphone 4: 3.582853

Benchmark (time to test word if it is in the dictionary or not):

-(BOOL)checkWord:(NSString *)word{

    NSDate *start = [NSDate date];

    BOOL yesNoMaybeSo = [englishDictionary containsObject:word];

    NSLog(@"Time to check word:\t%f",[start timeIntervalSinceNow]*-1.);
    return yesNoMaybeSo;

}

iphone 5: 0.000021 (seconds)

ipad 1: 0.000037

iphone 4: 0.000043

Answer 1

The most efficient way is probably to use a NSSet to store all the words you want to compare against your string.

Then you simply check whether your word belongs to the set like follows

BOOL englishWord = [theEnglishSet containsObject:yourString];

This will take constant time to perform.