add solution of problem 367: valid perfect square

Author: ppulse

ValidPerfectSquare367/README.md

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+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
+```

ValidPerfectSquare367/Solution.java

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+public class Solution {
+    public boolean isPerfectSquare(int num) {
+        if (num <= 0)
+            return false;
+        else if (num == 1)
+            return true;
+        
+        long left = 0;
+        long right = num;
+        
+        while (left < right) {
+            long mid = (left + right) >> 1;
+            long value = mid * mid;
+            
+            if (left == mid && value != num)
+                return false;
+            
+            if (value > num)
+                right = mid;
+            else if (value < num)
+                left = mid;
+            else
+                return true;
+        }
+        
+        return false;
+    }
+}