adding lecture 5 notes

lectures/05_classes_II/README.md

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+# Lecture 5 ---  Classes II: Sort, Non-member Operators
+
+- Classes in C++;
+- Non-member operators
+
+## 5.1 C++ Classes
+
+- Nuances to remember
+
+  - Within class scope (within the code of a member function) member variables and member functions of
+that class may be accessed without providing the name of the class object.  
+  - Within a member function, when an object of the same class type has been passed as an argument, direct
+access to the private member variables of that object is allowed (using the ’.’ notation).
+
+## 5.2 Exercises
+
+- [Leetcode problem 905: Sort Array By Parity](https://leetcode.com/problems/sort-array-by-parity/). Solution: [p905_sortarraybyparity.cpp](../../leetcode/p905_sortarraybyparity.cpp)
+- [Leetcode problem 977: Squares of a Sorted Array](https://leetcode.com/problems/squares-of-a-sorted-array/). Solution: [p977_sortedsquare.cpp](../../leetcode/p977_sortedsquare.cpp)
+- [Leetcode problem 1051: Height Checker](https://leetcode.com/problems/height-checker/). Solution: [p1051_heightchecker.cpp](../../leetcode/p1051_heightchecker.cpp)