Create valid-perfect-square.cpp

Author: kamyu104

C++/valid-perfect-square.cpp

@@ -0,0 +1,18 @@
+// Time:  O(logn)
+// Space: O(1)
+
+class Solution {
+public:
+    bool isPerfectSquare(int num) {
+        int left = 1, right = num;
+        while (left <= right) {
+            const int mid = left + (right - left) / 2;
+            if (mid >= num / mid) {
+                right = mid - 1;
+            } else {
+                left = mid + 1;
+            }
+        }
+        return left == num / left && num % left == 0;
+    }
+};