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src/main/java/io/zipcoder/Problem1.java

@@ -1,4 +1,30 @@
 package io.zipcoder;
 
+import java.util.HashMap;
+
 public class Problem1 {
+
+    private HashMap <Character, Character> characterMap = new HashMap<Character, Character>();
+
+    public Problem1() {
+        characterMap.put('f', '7');
+        characterMap.put('s', '$');
+        characterMap.put('1', '!');
+        characterMap.put('a', '@');
+    }
+
+    public String replaceCharacters(String stringToReplace){
+
+        char[] charArray = stringToReplace.toCharArray();
+
+        for (int i = 0; i < charArray.length; i++){
+            char charToReplace = charArray[i];
+            if (characterMap.containsKey(Character.toLowerCase(charToReplace))){
+                charArray[i] = characterMap.get(Character.toLowerCase(charToReplace));
+            }
+        }
+
+        return new String(charArray);
+    }
+
 }

src/test/java/io/zipcoder/Problem1Test.java

@@ -1,4 +1,25 @@
 package io.zipcoder;
 
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Test;
+
 public class Problem1Test {
+
+    private Problem1 problem1;
+    private String stringToTest;
+
+    @Before
+    public void setUp(){
+        problem1 = new Problem1();
+        stringToTest = "The Farmer went to the store to get 1 dollar's worth of fertilizer";
+    }
+
+    @Test
+    public void replaceCharactersTest(){
+        String expected = "The 7@rmer went to the $tore to get ! doll@r'$ worth o7 7ertilizer";
+        String actual = problem1.replaceCharacters(stringToTest);
+        Assert.assertEquals(expected, actual);
+
+    }
 }