From 32aef4e595dd6197bb05f54a0b1ae0875ea06346 Mon Sep 17 00:00:00 2001
From: Dmitry Kokorin <dmitry@kokorin.org>
Date: Thu, 7 Apr 2016 15:39:30 +0300
Subject: [PATCH] trinary: initial commit

---
 cpp/trinary/trinary.cpp | 35 +++++++++++++++++++++++++++++++++++
 cpp/trinary/trinary.h   | 11 +++++++++++
 2 files changed, 46 insertions(+)
 create mode 100644 cpp/trinary/trinary.cpp
 create mode 100644 cpp/trinary/trinary.h

diff --git a/cpp/trinary/trinary.cpp b/cpp/trinary/trinary.cpp
new file mode 100644
index 0000000..271cae7
--- /dev/null
+++ b/cpp/trinary/trinary.cpp
@@ -0,0 +1,35 @@
+#include "trinary.h"
+
+namespace trinary {
+
+namespace {
+
+inline bool is_digit(char ch)
+{
+    return ch >= '0' && ch <= '2';
+}
+
+inline int digit_to_decimal(char ch)
+{
+    return ch - '0';
+}
+
+}
+
+int to_decimal(const std::string &input)
+{
+    int result = 0;
+
+    for (auto ch : input) {
+
+        if (!is_digit(ch))
+            return 0;
+
+        result *= 3;
+        result += digit_to_decimal(ch);
+    }
+
+    return result;
+}
+
+}
diff --git a/cpp/trinary/trinary.h b/cpp/trinary/trinary.h
new file mode 100644
index 0000000..4e36773
--- /dev/null
+++ b/cpp/trinary/trinary.h
@@ -0,0 +1,11 @@
+#pragma once
+
+#define EXERCISM_RUN_ALL_TESTS
+
+#include <string>
+
+namespace trinary {
+
+int to_decimal(const std::string &input);
+
+}