CTCI 6.09: Lockers.groovy

src/main/groovy/Ch06_MathAndLogicPuzzles/_06_09_Lockers.groovy

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+package Ch06_MathAndLogicPuzzles
+
+/** Given closed lockers, by opening everyone, closing every second, opening every third, etc, which lockers will be open at the end? */
+class _06_09_Lockers {
+    static openLockers(int lockerCount) {
+        def results = new BitSet()
+
+        def lockerRange = 0..lockerCount
+        for (step in lockerRange)
+            lockerRange.step(step + 1) { results.flip(it) }
+
+        results.stream().collect()
+    }
+}

src/test/groovy/Ch06_MathAndLogicPuzzles/_06_09_LockersTest.groovy

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+package Ch06_MathAndLogicPuzzles
+
+import spock.lang.Specification
+import spock.lang.Unroll
+
+import static Ch06_MathAndLogicPuzzles._06_09_Lockers.openLockers
+import static java.lang.Math.sqrt
+
+@Unroll class _06_09_LockersTest extends Specification {
+    /*@formatter:off*/
+    def 'lockers?'() {
+        expect: openLockers(lockerCount) == result
+        where:  lockerCount || result
+                100         || (0..sqrt(lockerCount)).collect{ it**2 }        
+    }
+    /*@formatter:on*/
+}