NSString-Levenshtein.m

//
//  NSString-Levenshtein.m
//  https://web.archive.org/web/20031221230916/http://www.merriampark.com:80/ldobjc.htm
//  Created by Rick Bourner on Sat Aug 09 2003.
//  Rick@Bourner.com


@implementation NSString(Levenshtein)

// calculate the distance between two string treating them eash as a
// single word
- (float) compareWithWord: (NSString *) stringB
{
    // normalize strings
    NSString * stringA = [NSString stringWithString: self];
    [stringA stringByTrimmingCharactersInSet:
     [NSCharacterSet whitespaceAndNewlineCharacterSet]];
    [stringB stringByTrimmingCharactersInSet:
     [NSCharacterSet whitespaceAndNewlineCharacterSet]];
    stringA = [stringA lowercaseString];
    stringB = [stringB lowercaseString];
    
    
    // Step 1
    unsigned int k, i, j, cost, * d, distance;
    
    NSUInteger n = [stringA length];
    NSUInteger m = [stringB length];
    
    if( n++ != 0 && m++ != 0 ) {
        
        d = malloc( sizeof(unsigned int) * m * n );
        
        // Step 2
        for( k = 0; k < n; k++)
            d[k] = k;
        
        for( k = 0; k < m; k++)
            d[ k * n ] = k;
        
        // Step 3 and 4
        for( i = 1; i < n; i++ )
            for( j = 1; j < m; j++ ) {
                
                // Step 5
                if( [stringA characterAtIndex: i-1] ==
                   [stringB characterAtIndex: j-1] )
                    cost = 0;
                else
                    cost = 1;
                
                // Step 6
                d[ j * n + i ] = [self smallestOf: d [ (j - 1) * n + i ] + 1
                                            andOf: d[ j * n + i - 1 ] +  1
                                            andOf: d[ (j - 1) * n + i -1 ] + cost ];
            }
        
        distance = d[ n * m - 1 ];
        
        free( d );
        
        return distance;
    }
    return 0.0;
}


// return the minimum of a, b and c
- (int) smallestOf: (int) a andOf: (int) b andOf: (int) c
{
    int min = a;
    if( b < min )
        min = b;
    
    if( c < min )
        min = c;
    
    return min;
}

@end