Power-n

Change-Id: I82e6ca7e7b9e6831cb65171e1a21d9380f1a1d3b

Author: applewjg

Pow(x,n).java

@@ -0,0 +1,23 @@
+/*
+ Author:     King, [email protected]
+ Date:       Dec 25, 2014
+ Problem:    Pow(x, n)
+ Difficulty: easy
+ Source:     https://oj.leetcode.com/problems/powx-n/
+ Notes:
+ Implement pow(x, n).
+ 
+ Solution: recursion.
+ */
+public class Solution {
+    public double pow(double x, int n) {
+        if (x < 0) return (n % 2 == 0) ? pow(-x, n) : -pow(-x, n);
+        if (x == 0 || x == 1) return x;
+        if (n < 0) return 1.0 / pow(x,-n);
+        if (n == 0) return 1.0;
+        if (n == 1) return x;
+        double half = pow(x,n/2);
+        if (n % 2 == 0) return half * half;
+        else return x * half * half;
+    }
+}