add 319

fishercoder1534 · fishercoder1534 · commit 46564584db88 · 2017-06-06T22:53:19.000-07:00
diff --git a/README.md b/README.md
@@ -217,6 +217,7 @@ Your ideas/fixes/algorithms are more than welcome!
 |322|[Coin Change](https://leetcode.com/problems/coin-change/)|[Solution](../master/src/main/java/com/fishercoder/solutions/CoinChange.java)| O(?)|O(?) | Medium|
 |321|[Create Maximum Number](https://leetcode.com/problems/create-maximum-number/)|[Solution](../master/src/main/java/com/fishercoder/solutions/CreateMaximumNumber.java)| O(?)|O(?) | Hard
 |320|[Generalized Abbreviation](https://leetcode.com/problems/generalized-abbreviation/)|[Solution](../master/src/main/java/com/fishercoder/solutions/GeneralizedAbbreviation.java)| O(n*2^n)|O(n) | Medium| Backtracking, Bit Manipulation
+|319|[Bulb Switcher](https://leetcode.com/problems/bulb-switcher/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_319.java)| O(1)|O(1) | Medium| Brainteaser
 |317|[Shortest Distance from All Buildings](https://leetcode.com/problems/shortest-distance-from-all-buildings/)|[Solution](../master/src/main/java/com/fishercoder/solutions/ShortestDistanceFromAllBuildings.java)| O(?)|O(?) | Hard| 
 |316|[Remove Duplicate Letters](https://leetcode.com/problems/remove-duplicate-letters/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_316.java)| O(n)|O(1)| Hard| Stack, Recursion, Greedy
 |315|[Count of Smaller Numbers After Self](https://leetcode.com/problems/count-of-smaller-numbers-after-self/)|[Solution](../master/src/main/java/com/fishercoder/solutions/CountOfSmallerNumbersAfterSelf.java)| O(?)|O(?)| Hard| Tree
diff --git a/src/main/java/com/fishercoder/solutions/_319.java b/src/main/java/com/fishercoder/solutions/_319.java
@@ -0,0 +1,30 @@
+package com.fishercoder.solutions;
+
+/**
+ * 319. Bulb Switcher
+ *
+ * There are n bulbs that are initially off. You first turn on all the bulbs.
+ * Then, you turn off every second bulb. On the third round,
+ * you toggle every third bulb (turning on if it's off or turning off if it's on).
+ * For the ith round, you toggle every i bulb. For the nth round, you only
+ * toggle the last bulb. Find how many bulbs are on after n rounds.
+
+ Example:
+
+ Given n = 3.
+
+ At first, the three bulbs are [off, off, off].
+ After first round, the three bulbs are [on, on, on].
+ After second round, the three bulbs are [on, off, on].
+ After third round, the three bulbs are [on, off, off].
+
+ So you should return 1, because there is only one bulb is on.
+ */
+public class _319 {
+
+    public int bulbSwitch(int n) {
+        if (n < 2) return n;
+        return (int) Math.sqrt(n);
+    }
+
+}
diff --git a/src/test/java/com/fishercoder/_319Test.java b/src/test/java/com/fishercoder/_319Test.java
@@ -0,0 +1,76 @@
+package com.fishercoder;
+
+import com.fishercoder.solutions._319;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+/**
+ * Created by stevesun on 6/6/17.
+ */
+public class _319Test {
+    private static _319 test;
+
+    @BeforeClass
+    public static void setup(){
+        test = new _319();
+    }
+
+    @Test
+    public void test1(){
+        assertEquals(1, test.bulbSwitch(2));
+    }
+
+    @Test
+    public void test2(){
+        assertEquals(1, test.bulbSwitch(3));
+    }
+
+    @Test
+    public void test3(){
+        assertEquals(2, test.bulbSwitch(4));
+    }
+
+    @Test
+    public void test4(){
+        assertEquals(2, test.bulbSwitch(5));
+    }
+
+    @Test
+    public void test5(){
+        assertEquals(2, test.bulbSwitch(6));
+    }
+
+    @Test
+    public void test6(){
+        assertEquals(2, test.bulbSwitch(7));
+    }
+
+    @Test
+    public void test7(){
+        assertEquals(2, test.bulbSwitch(8));
+    }
+
+    @Test
+    public void test8(){
+        assertEquals(3, test.bulbSwitch(9));
+    }
+
+    @Test
+    public void test11(){
+        assertEquals(3, test.bulbSwitch(15));
+    }
+
+    @Test
+    public void test9(){
+        assertEquals(4, test.bulbSwitch(17));
+    }
+
+    @Test
+    public void test10(){
+        assertEquals(4, test.bulbSwitch(16));
+    }
+
+
+}
