Create valid-perfect-square.py

Python/valid-perfect-square.py

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+# Time:  O(logn)
+# Space: O(1)
+
+# Given a positive integer num, write a function
+# which returns True if num is a perfect square else False.
+#
+# Note: Do not use any built-in library function such as sqrt.
+#
+# Example 1:
+#
+# Input: 16
+# Returns: True
+# Example 2:
+#
+# Input: 14
+# Returns: False
+
+class Solution(object):
+    def isPerfectSquare(self, num):
+        """
+        :type num: int
+        :rtype: bool
+        """
+        left, right = 1, num
+        while left <= right:
+            mid = left + (right - left) / 2
+            if mid >= num / mid:
+                right = mid - 1
+            else:
+                left = mid + 1
+        return left == num / left and num % left == 0