words: new package Damerau Levenshtein distance function. (#3929)

pkg/words/damerau-levenshtein.go

@@ -0,0 +1,64 @@
+/*
+ * Minio Client (C) 2014, 2015, 2016, 2017 Minio, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package words
+
+import "math"
+
+// Returns the minimum value of a slice of integers
+func minimum(integers []int) (minVal int) {
+	minVal = math.MaxInt32
+	for _, v := range integers {
+		if v < minVal {
+			minVal = v
+		}
+	}
+	return
+}
+
+// DamerauLevenshteinDistance calculates distance between two strings using an algorithm
+// described in https://en.wikipedia.org/wiki/Damerau-Levenshtein_distance
+func DamerauLevenshteinDistance(a string, b string) int {
+	var cost int
+	d := make([][]int, len(a)+1)
+	for i := 1; i <= len(a)+1; i++ {
+		d[i-1] = make([]int, len(b)+1)
+	}
+	for i := 0; i <= len(a); i++ {
+		d[i][0] = i
+	}
+	for j := 0; j <= len(b); j++ {
+		d[0][j] = j
+	}
+	for i := 1; i <= len(a); i++ {
+		for j := 1; j <= len(b); j++ {
+			if a[i-1] == b[j-1] {
+				cost = 0
+			} else {
+				cost = 1
+			}
+			d[i][j] = minimum([]int{
+				d[i-1][j] + 1,
+				d[i][j-1] + 1,
+				d[i-1][j-1] + cost,
+			})
+			if i > 1 && j > 1 && a[i-1] == b[j-2] && a[i-2] == b[j-1] {
+				d[i][j] = minimum([]int{d[i][j], d[i-2][j-2] + cost}) // transposition
+			}
+		}
+	}
+	return d[len(a)][len(b)]
+}