Ternary number

tdd_intro/homework/02_ternary_numbers/test.cpp

@@ -16,3 +16,71 @@ The last place in a ternary number is the 1's place. The second to last is the 3
 
 If your language provides a method in the standard library to perform the conversion, pretend it doesn't exist and implement it yourself.
 */
+
+const int s_ternary_base = 3;
+const int s_ascii_shift = 48;
+
+bool IsValidTernaryDigit(int digit)
+{
+     return (digit <= 3 && digit >= 0);
+}
+
+long long ConvertTernaryToDecimal(const std::string& ternaryNumber)
+{
+    long long sum = 0;
+    long long value = 1;
+    int numberLen = ternaryNumber.length();
+
+    for(int i = numberLen - 1; i >= 0; --i)
+    {
+        int currentSymbol = static_cast<int>(ternaryNumber[i]) - s_ascii_shift;
+        if(!IsValidTernaryDigit(currentSymbol))
+        {
+            return 0;
+        }
+
+        sum += currentSymbol * value;
+        value *= s_ternary_base;
+    }
+
+    return sum;
+}
+
+
+TEST(TernaryNumber, OneConvertsToOneTest)
+{
+    EXPECT_EQ(1, ConvertTernaryToDecimal("1"));
+}
+
+TEST(TernaryNumber, ConvertValidTernaryNumberTest)
+{
+    EXPECT_EQ(5, ConvertTernaryToDecimal("012"));
+}
+
+TEST(TernaryNumber, ConvertAnotherValidTernaryNumberTest)
+{
+    EXPECT_EQ(302, ConvertTernaryToDecimal("102012"));
+}
+
+TEST(TernaryNumber, InvalidTernaryNumberTest)
+{
+    EXPECT_EQ(0, ConvertTernaryToDecimal("502012"));
+}
+
+TEST(TernaryNumber, BigTernaryNumberTest)
+{
+    EXPECT_EQ(10460353203, ConvertTernaryToDecimal("1000000000000000000000"));
+}
+
+TEST(TernaryNumber, IsValidTernaryDigitNegativeTest)
+{
+    EXPECT_FALSE(IsValidTernaryDigit(-45));
+}
+
+TEST(TernaryNumber, AcceptanceTest)
+{
+    EXPECT_EQ(0, ConvertTernaryToDecimal("0"));
+    EXPECT_EQ(12, ConvertTernaryToDecimal("33"));
+    EXPECT_EQ(0, ConvertTernaryToDecimal("567"));
+    EXPECT_EQ(0, ConvertTernaryToDecimal("(567)bh"));
+}