Case-insensitive Levenshtein Distance Implementation

gistfile1.go

// runeAt returns the unicode rune at the specified index.
func runeAt(s string, index int) rune {
	i := 0
	for _, c := range s {
		if i == index {
			return c
		}
		i++
	}
	return -1
}

// compare returns the edit distance between two given strings
// using a modified, case-insensitive version of the Levenshtein
// distance algorithm.
func compare(a, b string) int {
	a = strings.ToLower(a)
	b = strings.ToLower(b)
	a_len := utf8.RuneCountInString(a)
	b_len := utf8.RuneCountInString(b)
	d := make([][]int, a_len+1)
	for i := 0; i < len(d); i++ {
		d[i] = make([]int, b_len+1)
	}
	for i := 0; i < len(d); i++ {
		d[i][0] = i
	}
	for i := 0; i < len(d[0]); i++ {
		d[0][i] = i
	}
	for i := 1; i < len(d); i++ {
		for j := 1; j < len(d[0]); j++ {
			if runeAt(a, i-1) == runeAt(b, j-1) {
				d[i][j] = d[i-1][j-1]
			} else if i > 1 && j > 1 && runeAt(a, i-1) == runeAt(b, j-2) && runeAt(a, i-2) == runeAt(b, j-1) {
				min1 := d[i-2][j-2] + 1
				min2 := d[i-1][j] + 1
				min3 := d[i][j-1] + 1
				min4 := d[i-1][j-1] + 1
				d[i][j] = int(math.Min(math.Min(float64(min1), float64(min2)), math.Min(float64(min3), float64(min4))))
			} else {
				min1 := d[i-1][j] + 1
				min2 := d[i][j-1] + 1
				min3 := d[i-1][j-1] + 1
				d[i][j] = int(math.Min(math.Min(float64(min1), float64(min2)), float64(min3)))
			}
		}
	}
	return d[a_len][b_len]
}