add new solutions

solutions/0/q17/solution.go

@@ -0,0 +1,39 @@
+package q17
+
+var alphabets = [][]byte{
+	[]byte("abc"),
+	[]byte("def"),
+	[]byte("ghi"),
+	[]byte("jkl"),
+	[]byte("mno"),
+	[]byte("pqrs"),
+	[]byte("tuv"),
+	[]byte("wxyz"),
+}
+
+func combinations(offsets []int, i int, buffer []byte, strings []string) []string {
+	if buffer == nil {
+		buffer = make([]byte, len(offsets))
+	}
+
+	if i == len(offsets) {
+		return append(strings, string(buffer))
+	}
+
+	for _, c := range alphabets[offsets[i]] {
+		buffer[i] = c
+		strings = combinations(offsets, i+1, buffer, strings)
+	}
+	return strings
+}
+
+func letterCombinations(digits string) []string {
+	offsets := make([]int, len(digits))
+	for i := range len(digits) {
+		offsets[i] = int(digits[i] - '2')
+	}
+
+	return combinations(offsets, 0, nil, []string{})
+}
+
+var _ = letterCombinations