Levenshtein — swift

gistfile1.txt

/**
 * Levenshtein edit distance calculator
 * Usage: levenstein <string> <string>
 *
 * Inspired by https://gist.github.com/bgreenlee/52d93a1d8fa1b8c1f38b
 * Improved with http://stackoverflow.com/questions/26990394/slow-swift-arrays-and-strings-performance
 */

class Tools {

    private class func min(numbers: Int...) -> Int {
        return numbers.reduce(numbers[0], combine: {$0 < $1 ? $0 : $1})
    }
    
    class Array2D {
        var cols:Int, rows:Int
        var matrix: [Int]
        
        
        init(cols:Int, rows:Int) {
            self.cols = cols
            self.rows = rows
            matrix = Array(count:cols*rows, repeatedValue:0)
        }
        
        subscript(col:Int, row:Int) -> Int {
            get {
                return matrix[cols * row + col]
            }
            set {
                matrix[cols*row+col] = newValue
            }
        }
        
        func colCount() -> Int {
            return self.cols
        }
        
        func rowCount() -> Int {
            return self.rows
        }
    }
    
    class func levenshtein(aStr: String, bStr: String) -> Int {
        let a = Array(aStr.utf16)
        let b = Array(bStr.utf16)
        
        var dist = Array2D(cols: a.count + 1, rows: b.count + 1)
        
        for i in 1...a.count {
            dist[i, 0] = i
        }
        
        for j in 1...b.count {
            dist[0, j] = j
        }
        
        for i in 1...a.count {
            for j in 1...b.count {
                if a[i-1] == b[j-1] {
                    dist[i, j] = dist[i-1, j-1]  // noop
                } else {
                    dist[i, j] = min(
                        dist[i-1, j] + 1,  // deletion
                        dist[i, j-1] + 1,  // insertion
                        dist[i-1, j-1] + 1  // substitution
                    )
                }
            }
        }
        
        return dist[a.count, b.count]
    }

    
}

Statements like this for i in 1...a.count will lead to crash if a.count is 0.

Always use something like 1..<count to avoid any possibility of crashing.