added doubloon examples

ChrisMayfield · ChrisMayfield · commit edd4f88fbb02 · 2017-08-05T12:46:31.000-04:00
diff --git a/ch07/Doubloon.java b/ch07/Doubloon.java
@@ -0,0 +1,30 @@
+/**
+ * Example from the end of Chapter 7.
+ */
+public class Doubloon {
+    
+    public static boolean isDoubloon(String s) {
+        
+        // count the number of times each letter appears
+        int[] counts = new int[26];
+        String lower = s.toLowerCase();
+        for (char letter : lower.toCharArray()) {
+            int index = letter - 'a';
+            counts[index]++;
+        }
+        
+        // determine whether the given word is a doubloon
+        for (int count : counts) {
+            if (count != 0 && count != 2) {
+                return false;
+            }
+        }
+        return true;
+    }
+    
+    public static void main(String[] args) {
+        System.out.println(isDoubloon("Mama"));
+        System.out.println(isDoubloon("Lama"));
+    }
+    
+}
diff --git a/ch07/Inefficient.java b/ch07/Inefficient.java
@@ -0,0 +1,31 @@
+/**
+ * Version of Doubloon that uses nested loops.
+ */
+public class Inefficient {
+    
+    public static boolean isDoubloon(String s) {
+        
+        // count the number of times each letter appears
+        s = s.toLowerCase();
+        for (char c = 'a'; c <= 'z'; c++) {
+            int count = 0;
+            for (int i = 0; i < s.length(); i++) {
+                if (s.charAt(i) == c) {
+                    count++;
+                }
+            }
+            
+            // determine whether the word is a doubloon
+            if (count != 0 && count != 2) {
+                return false;  // not a doubloon
+            }
+        }
+        return true;  // all counts were 0 or 2
+    }
+    
+    public static void main(String[] args) {
+        System.out.println(isDoubloon("Mama"));
+        System.out.println(isDoubloon("Lama"));
+    }
+    
+}
