Updates 50_powx,_n__medium.md

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Author: cheonhyangzhang

50_powx,_n__medium.md

@@ -19,7 +19,8 @@ It could be faster to be O(lgn) using divide and conquer.
 
 ### Solutions:
 
-
+Note:
+-Integer.MIN_VALUE = Integer.MIN_VALUE
 
 ```java
 public class Solution {
@@ -43,4 +44,27 @@ public class Solution {
         }
     }//power
 }
+```
+
+```java
+class Solution {
+    public double myPow(double x, int n) {
+        return pow(x, n);
+    }
+    private double pow(double x, long n) {
+        if (n == 0) {
+            return 1;
+        }
+        if (n < 0) {
+            return 1 / pow(x, -n);
+        }
+        double v = pow(x, n / 2);
+        if (n % 2 == 0) {
+            return v*v;
+        }
+        else {
+            return v*v*x;
+        }
+    }
+}
 ```