Update and rename Power of four.java to Power of Four.java

Author: varunu28

Easy/Power of Four.java

@@ -0,0 +1,19 @@
+class Solution {
+  public boolean isPowerOfFour(int n) {
+    long left = 0;
+    long right = n / 2 + 1;
+    while (left <= right) {
+      long mid = (left + right) / 2;
+      long pow = (long) (Math.pow(4, mid));
+      if (pow == ((long) n)) {
+        return true;
+      }
+      if (pow > ((long) n)) {
+        right = mid - 1;
+      } else {
+        left = mid + 1;
+      }
+    }
+    return false;
+  }
+}