CTCI 6.07: TheApocalypse.groovy

src/main/groovy/Ch06_MathAndLogicPuzzles/_06_07_TheApocalypse.groovy

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+package Ch06_MathAndLogicPuzzles
+
+import static Ch06_MathAndLogicPuzzles._06_07_TheApocalypse.Gender.FEMALE
+
+/** What would be the ratio of men/women, if people would stop having children immediately after having a girl? 
+ * 1/2 would have 1 girl
+ * 1/4 would have 1 boy and 1 girl
+ * 1/8 would have 2 boys and 1 girl
+ * 1/16 would have 3 boys and 1 girl
+ * ...
+ * boy/girl ratio = 0/2 + 1/4 + 2/8 + 3/16 + ... (n-1)/2**n == 1 for n→∞  
+ * */
+class _06_07_TheApocalypse {
+    static ratio(int familyCount) {
+        def (males, females) = [familyCount, familyCount]
+        (1..familyCount).each {
+            while (Gender.random != FEMALE)
+                males++
+            females++
+        }
+        males / females
+    }
+
+    private static enum Gender {
+        MALE, FEMALE
+
+        private static rand = new Random()
+        static getRandom() {
+            def genders = values()
+            genders[rand.nextInt(genders.size())]
+        }
+    }
+}

src/test/groovy/Ch06_MathAndLogicPuzzles/_06_07_TheApocalypseTest.groovy

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+package Ch06_MathAndLogicPuzzles
+
+import spock.lang.Specification
+import spock.lang.Unroll
+
+import static Ch06_MathAndLogicPuzzles._06_07_TheApocalypse.ratio
+import static java.lang.Math.abs
+
+@Unroll class _06_07_TheApocalypseTest extends Specification {
+    /*@formatter:off*/
+    def 'theApocalypse?'() {
+        expect: (500..1000).each { familyCount -> 
+                    def result = ratio(familyCount)
+                    assert abs(result - 1) < 2/10
+                }
+    }
+    /*@formatter:on*/
+}