go: add «647. Palindromic Substrings»

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

go/palindromic-substrings.go

@@ -0,0 +1,27 @@
+func checkSubstring(s string, i, j int) int {
+	if i < 0 || j >= len(s) {
+		return 0
+	}
+
+	count := 0
+
+	for i >= 0 && j < len(s) && s[i] == s[j] {
+		count += 1
+
+		i -= 1
+		j += 1
+	}
+
+	return count
+}
+
+func countSubstrings(s string) int {
+	count := 0
+
+	for i, _ := range s {
+		count += checkSubstring(s, i, i)
+		count += checkSubstring(s, i, i+1)
+	}
+
+	return count
+}