Add new execise hexadecimal

config.json

@@ -31,6 +31,7 @@
     "crypto-square",
     "trinary",
     "rna-transcription",
+    "hexadecimal",
     "sieve",
     "simple-cipher",
     "octal",

hexadecimal/build.gradle

@@ -0,0 +1,11 @@
+apply plugin: "java"
+apply plugin: "eclipse"
+apply plugin: "idea"
+
+repositories {
+  mavenCentral()
+}
+
+dependencies {
+  testCompile "junit:junit:4.10"
+}

hexadecimal/src/example/java/Hexadecimal.java

@@ -0,0 +1,15 @@
+import java.util.Arrays;
+
+public class Hexadecimal {
+    private static final String HEXES = "0123456789abcdef";
+    public static int toDecimal(String input){
+        boolean  isHex = input.matches("^[0-9a-f]+");
+        if (!isHex) return 0;
+        return Arrays.stream(input.split(""))
+                .map(HEXES::indexOf)
+                .reduce(0, (decimal, hex) -> decimal * 16 + hex);
+
+    }
+}
+
+

hexadecimal/src/test/java/HexadecimalTest.java

@@ -0,0 +1,65 @@
+import org.junit.Test;
+import static org.junit.Assert.assertEquals;
+
+public class HexadecimalTest {
+
+    @Test
+    public void testOne(){
+        int expected = 1;
+        assertEquals(expected, Hexadecimal.toDecimal("1"));
+    }
+
+    @Test
+    public void testC(){
+        int expected = 12;
+        assertEquals(expected, Hexadecimal.toDecimal("c"));
+    }
+
+    @Test
+    public void test10(){
+        int expected = 16;
+        assertEquals(expected, Hexadecimal.toDecimal("10"));
+    }
+
+    @Test
+    public void testAf(){
+        int expected = 175;
+        assertEquals(expected, Hexadecimal.toDecimal("af"));
+    }
+
+    @Test
+    public void test100(){
+        int expected = 256;
+        assertEquals(expected, Hexadecimal.toDecimal("100"));
+    }
+
+    @Test
+    public void test19ace(){
+        int expected = 105166;
+        assertEquals(expected, Hexadecimal.toDecimal("19ace"));
+    }
+
+    @Test
+    public void testInvalid(){
+        int expected = 0;
+        assertEquals(expected, Hexadecimal.toDecimal("carrot"));
+    }
+
+    @Test
+    public void testBlack(){
+        int expected = 0;
+        assertEquals(expected, Hexadecimal.toDecimal("000000"));
+    }
+
+    @Test
+    public void testWhite(){
+        int expected = 16777215;
+        assertEquals(expected, Hexadecimal.toDecimal("ffffff"));
+    }
+
+    @Test
+    public void testYellow(){
+        int expected = 16776960;
+        assertEquals(expected, Hexadecimal.toDecimal("ffff00"));
+    }
+}

settings.gradle

@@ -9,6 +9,7 @@ include 'etl'
 include 'gigasecond'
 include 'grade-school'
 include 'hamming'
+include 'hexadecimal'
 include 'hello-world'
 include 'luhn'
 include 'meetup'