refactor 509

fishercoder1534 · fishercoder1534 · commit abbf2eb05824 · 2019-12-02T06:38:30.000-08:00
diff --git a/src/main/java/com/fishercoder/solutions/_509.java b/src/main/java/com/fishercoder/solutions/_509.java
@@ -6,37 +6,37 @@
 /**
  * 509. Fibonacci Number
  *
- * The Fibonacci numbers, commonly denoted F(n) form a sequence, called the Fibonacci sequence, such that each number is the sum of the two preceding ones, starting from 0 and 1. That is,
+ * The Fibonacci numbers, commonly denoted F(n) form a sequence, called the Fibonacci sequence,
+ * such that each number is the sum of the two preceding ones, starting from 0 and 1. That is,
  *
  * F(0) = 0,   F(1) = 1
  * F(N) = F(N - 1) + F(N - 2), for N > 1.
  * Given N, calculate F(N).
  *
- *
- *
  * Example 1:
- *
  * Input: 2
  * Output: 1
  * Explanation: F(2) = F(1) + F(0) = 1 + 0 = 1.
- * Example 2:
  *
+ * Example 2:
  * Input: 3
  * Output: 2
  * Explanation: F(3) = F(2) + F(1) = 1 + 1 = 2.
- * Example 3:
  *
+ * Example 3:
  * Input: 4
  * Output: 3
  * Explanation: F(4) = F(3) + F(2) = 2 + 1 = 3.
  *
- *
  * Note:
- *
  * 0 ≤ N ≤ 30.
  */
 public class _509 {
   public static class Solution1 {
+    /**
+     * Time: O(n)
+     * Space: O(n)
+     */
     public int fib(int N) {
       List<Integer> list = new ArrayList<>();
       list.add(0);
@@ -47,4 +47,43 @@ public int fib(int N) {
       return list.get(N);
     }
   }
+
+  public static class Solution2 {
+    /**
+     * Time: O(n)
+     * Space: O(n)
+     */
+    public int fib(int N) {
+      if (N < 2) {
+        return N;
+      }
+      int[] fibNums = new int[N + 1];
+      fibNums[0] = 0;
+      fibNums[1] = 1;
+      for (int i = 2; i <= N; i++) {
+        fibNums[i] = fibNums[i - 1] + fibNums[i - 2];
+      }
+      return fibNums[N];
+    }
+  }
+
+  public static class Solution3 {
+    /**
+     * Time: O(n)
+     * Space: O(1)
+     */
+    public int fib(int N) {
+      if (N < 2) {
+        return N;
+      }
+      int a = 0;
+      int b = 1;
+      while (N-- > 1) {
+        int sum = a + b;
+        a = b;
+        b = sum;
+      }
+      return b;
+    }
+  }
 }
diff --git a/src/test/java/com/fishercoder/_509Test.java b/src/test/java/com/fishercoder/_509Test.java
@@ -7,30 +7,42 @@
 import static org.junit.Assert.assertEquals;
 
 public class _509Test {
-  private static _509.Solution1 solution1;
-
-  @BeforeClass
-  public static void setup() {
-    solution1 = new _509.Solution1();
-  }
-
-  @Test
-  public void test1() {
-    assertEquals(1, solution1.fib(2));
-  }
-
-  @Test
-  public void test2() {
-    assertEquals(2, solution1.fib(3));
-  }
-
-  @Test
-  public void test3() {
-    assertEquals(3, solution1.fib(4));
-  }
-
-  @Test
-  public void test4() {
-    assertEquals(0, solution1.fib(0));
-  }
+    private static _509.Solution1 solution1;
+    private static _509.Solution2 solution2;
+    private static _509.Solution3 solution3;
+
+    @BeforeClass
+    public static void setup() {
+        solution1 = new _509.Solution1();
+        solution2 = new _509.Solution2();
+        solution3 = new _509.Solution3();
+    }
+
+    @Test
+    public void test1() {
+        assertEquals(1, solution1.fib(2));
+        assertEquals(1, solution2.fib(2));
+        assertEquals(1, solution3.fib(2));
+    }
+
+    @Test
+    public void test2() {
+        assertEquals(2, solution1.fib(3));
+        assertEquals(2, solution2.fib(3));
+        assertEquals(2, solution3.fib(3));
+    }
+
+    @Test
+    public void test3() {
+        assertEquals(3, solution1.fib(4));
+        assertEquals(3, solution2.fib(4));
+        assertEquals(3, solution3.fib(4));
+    }
+
+    @Test
+    public void test4() {
+        assertEquals(0, solution1.fib(0));
+        assertEquals(0, solution2.fib(0));
+        assertEquals(0, solution3.fib(0));
+    }
 }
