@@ -0,0 +1,68 @@
+package com.github.mstepan.leetcode.medium;
+
+/**
+ * 319. Bulb Switcher
+ *
+ * <p>https://leetcode.com/problems/bulb-switcher/description/
+ */
+public class BulbSwitcher {
+
+    /**
+     * time: O(sqrt(N))
+     *
+     * <p>space: O(1)
+     */
+    public static int bulbSwitch(int n) {
+
+        if (n < 0) {
+            throw new IllegalArgumentException("Can't handle negative value");
+        }
+
+        if (n < 2) {
+            return n;
+        }
+
+        int leftSize = n;
+        int bitsSetCnt = 0;
+
+        for (int zerosCnt = 2; leftSize > 0; zerosCnt += 2) {
+            leftSize = leftSize - 1 - zerosCnt;
+            ++bitsSetCnt;
+        }
+
+        return bitsSetCnt;
+    }
+
+    //    public static void main(String[] args) {
+    //        for (int i = 0; i <= 100; ++i) {
+    //            System.out.printf("{%d}: %s%n", i, bulbSwitchString(i));
+    //        }
+    //    }
+    //
+    //    private static String bulbSwitchString(int n) {
+    //        if (n == 0) {
+    //            return "";
+    //        }
+    //
+    //        if (n == 1) {
+    //            return "1";
+    //        }
+    //
+    //        final boolean[] result = new boolean[n];
+    //        Arrays.fill(result, true);
+    //
+    //        for (int offset = 2; offset <= n; ++offset) {
+    //            for (int idx = offset - 1; idx < result.length; idx += offset) {
+    //                result[idx] = !result[idx];
+    //            }
+    //        }
+    //
+    //        StringBuilder resultAsStr = new StringBuilder(n);
+    //
+    //        for (boolean bit : result) {
+    //            resultAsStr.append(bit ? "1" : "0");
+    //        }
+    //
+    //        return resultAsStr.toString();
+    //    }
+}
@@ -0,0 +1,24 @@
+package com.github.mstepan.leetcode.medium;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import org.junit.jupiter.api.Test;
+
+public class BulbSwitcherTest {
+
+    @Test
+    void bulbSwitch() {
+        assertEquals(0, BulbSwitcher.bulbSwitch(0));
+        assertEquals(1, BulbSwitcher.bulbSwitch(1));
+        assertEquals(1, BulbSwitcher.bulbSwitch(2));
+        assertEquals(4, BulbSwitcher.bulbSwitch(16));
+    }
+
+    @Test
+    void bulbSwitchNegativeValueThrowsException() {
+        assertThrows(IllegalArgumentException.class, () -> BulbSwitcher.bulbSwitch(-1));
+        assertThrows(IllegalArgumentException.class, () -> BulbSwitcher.bulbSwitch(-5));
+        assertThrows(IllegalArgumentException.class, () -> BulbSwitcher.bulbSwitch(-133));
+    }
+}