go: add «72. Edit Distance»

Signed-off-by: Matej Focko <me@mfocko.xyz>

go/edit-distance.go

@@ -0,0 +1,60 @@
+package main
+
+const UNSET int = -1
+
+type Solver struct {
+	word1 string
+	word2 string
+	dp    [][]int
+}
+
+func makeSolver(word1, word2 string) Solver {
+	dp := make([][]int, len(word1))
+	for i := range len(word1) {
+		dp[i] = make([]int, len(word2))
+		for j := range len(word2) {
+			dp[i][j] = UNSET
+		}
+	}
+
+	return Solver{
+		word1: word1,
+		word2: word2,
+		dp:    dp,
+	}
+}
+
+func (s *Solver) solve(i, j int) int {
+	if i >= len(s.word1) {
+		return len(s.word2) - j
+	}
+
+	if j >= len(s.word2) {
+		return len(s.word1) - i
+	}
+
+	if s.dp[i][j] != UNSET {
+		return s.dp[i][j]
+	}
+
+	if s.word1[i] == s.word2[j] {
+		s.dp[i][j] = s.solve(i+1, j+1)
+	} else {
+		inserting := 1 + s.solve(i, j+1)
+		deleting := 1 + s.solve(i+1, j)
+		replacing := 1 + s.solve(i+1, j+1)
+
+		s.dp[i][j] = min(inserting, min(deleting, replacing))
+	}
+
+	return s.dp[i][j]
+}
+
+func (s *Solver) Solve() int {
+	return s.solve(0, 0)
+}
+
+func minDistance(word1 string, word2 string) int {
+	solver := makeSolver(word1, word2)
+	return solver.Solve()
+}