Merge pull request #365 from tspeng/fast-power

Fast power

Power of N/fastpower_n.py

@@ -0,0 +1,29 @@
+def fastpower(x, n): 
+    """
+    implement a fast power algorithm
+    x : any float number, which works in python2 and 3
+    n : any integer including negative
+    """
+    if(x == 0):
+        return 0.
+
+    if(n == 0):
+        return 1.0
+    # when n < 0, convert it to positve by taking the reciprocal of x
+    if(n < 0):
+        x = 1 / x
+        n = abs(n)
+
+    if(n % 2 == 0):
+        return fastpower(x, n // 2) ** 2
+    else:
+        return fastpower(x, (n - 1) // 2) ** 2 * x
+
+if __name__ == "__main__":
+    x = float(input("Please input the base: "))
+    n = int(input("Please input the power(int): "))
+
+    if(x == 0. and n == 0):
+        print("0 to the power of 0 is undefined")
+    else:
+        print("{} to the power of {} is : {}".format(x, n, fastpower(x, n)))