refactor 50

Author: fishercoder1534

src/main/java/com/fishercoder/solutions/_50.java

@@ -17,23 +17,53 @@
  */
 public class _50 {
 
-    public static class Solution1 {
-        public double myPow(double x, int n) {
-            if (n == 0) {
-                return 1;
-            }
-            if (n == Integer.MIN_VALUE) {
-                ++n;
-                n = -n;
-                x = 1 / x;
-                return x * x * myPow(x * x, n / 2);
-            }
-            if (n < 0) {
-                n = -n;
-                x = 1 / x;
-            }
-            return (n % 2 == 0) ? myPow(x * x, n / 2) : x * myPow(x * x, n / 2);
-        }
+  public static class Solution1 {
+    /**
+     * Time: O(logn)
+     * Space: O(logn)
+     */
+    public double myPow(double x, int n) {
+      long N = n;
+      if (N < 0) {
+        x = 1 / x;
+        N = -N;
+      }
+      return fastPow(x, N);
+    }
+
+    private double fastPow(double x, long n) {
+      if (n == 0) {
+        return 1.0;
+      }
+      double half = fastPow(x, n / 2);
+      if (n % 2 == 0) {
+        return half * half;
+      } else {
+        return half * half * x;
+      }
     }
+  }
 
+  public static class Solution2 {
+    /**
+     * Time: O(logn)
+     * Space: O(1)
+     */
+    public double myPow(double x, int n) {
+      long N = n;
+      if (N < 0) {
+        x = 1 / x;
+        N = -N;
+      }
+      double answer = 1;
+      double currentProduct = x;
+      for (long i = N; i > 0; i /= 2) {
+        if (i % 2 == 1) {
+          answer = answer * currentProduct;
+        }
+        currentProduct *= currentProduct;
+      }
+      return answer;
+    }
+  }
 }

src/test/java/com/fishercoder/_50Test.java

@@ -0,0 +1,24 @@
+package com.fishercoder;
+
+import com.fishercoder.solutions._50;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class _50Test {
+  private static _50.Solution1 solution1;
+  private static _50.Solution2 solution2;
+
+  @BeforeClass
+  public static void setup() {
+    solution1 = new _50.Solution1();
+    solution2 = new _50.Solution2();
+  }
+
+  @Test
+  public void test1() {
+    assertEquals(1024.00000, solution1.myPow(2.00000, 10), 0.00001);
+    assertEquals(1024.00000, solution2.myPow(2.00000, 10), 0.00001);
+  }
+}