Add longest common subsequence algorithm and concomitant tests.

longestcommonsubsequence.go

@@ -0,0 +1,30 @@
+package matchr
+
+// LongestCommonSubsequence computes the longest substring
+// between two strings. The returned value is the length
+// of the substring, which contains letters from both
+// strings, while maintaining the order of the letters.
+func LongestCommonSubsequence(s1, s2 string) int {
+	r1 := []rune(s1)
+	r2 := []rune(s2)
+	table := make([][]int, len(s1)+1)
+
+	// Construct 2D table
+	for i := range table {
+		table[i] = make([]int, len(s2)+1)
+	}
+
+	var i int
+	var j int
+
+	for i = len(r1) - 1; i >= 0; i-- {
+		for j = len(r2) - 1; j >= 0; j-- {
+			if r1[i] == r2[j] {
+				table[i][j] = 1 + table[i+1][j+1]
+			} else {
+				table[i][j] = maxI(table[i+1][j], table[i][j+1])
+			}
+		}
+	}
+	return table[0][0]
+}

longestcommonsubsequence_test.go

@@ -0,0 +1,33 @@
+package matchr
+
+import "testing"
+
+var lcstests = []struct {
+	s1     string
+	s2     string
+	length int
+}{
+	// match beginning
+	{"cans", "can", 3},
+	// match end
+	{"ebay", "bay", 3},
+	// gap in the middle
+	{"coins", "cons", 4},
+	// one empty, left
+	{"", "hello", 0},
+	// one empty, right
+	{"goodbye", "", 0},
+	// two empties
+	{"", "", 0},
+	// unicode stuff!
+	{"Schüßler", "Schüßler", 8},
+}
+
+func TestLongestCommonSubsequence(t *testing.T) {
+	for _, tt := range lcstests {
+		length := LongestCommonSubsequence(tt.s1, tt.s2)
+		if length != tt.length {
+			t.Errorf("LongestCommonSubsequence('%s', '%s') = %v, want %v", tt.s1, tt.s2, length, tt.length)
+		}
+	}
+}