C++ standard containers, iterators and algorithm contracts
Choose by the required operations
A container supplies a data representation with particular access, insertion, invalidation and complexity properties. A vector supports contiguous storage and random access, while growth can reallocate and invalidate relevant references and iterators. Reserve changes available capacity, not the element count, and a request does not universally require an exact capacity equal to the requested number. A list supports different iterator and insertion behavior. A map orders by its comparison relation; an unordered container has different average and worst-case lookup considerations.
Check range and iterator requirements
Standard algorithms operate on specified ranges, commonly using an included beginning and excluded end. Dereferencing end is not a valid way to read an element. Iterator categories describe supported operations and guarantees. std::sort requires random-access iterators, while a list provides its own supported sorting member. The standard contract, not one library’s internal sorting algorithm, defines the portable requirement. A comparison relation must satisfy the relevant ordering conditions; using less-than-or-equal as a general sort comparator is not a valid substitute.
Separate logical and physical modification
The remove algorithm rearranges kept elements and returns a logical new end; it does not itself shrink the container. The erase-remove idiom combines that result with a suitable container erase. Unique removes adjacent equivalent repetitions logically, so nonadjacent duplicates require different preparation or a different method. Sorting, merging, set operations and binary searching have actual range/order prerequisites. A lower-bound result can be end, so check before reading through it.
Interpret numerical and complexity claims
An accumulate operation uses its initial value and operation, which influence both result and type. Multiplicative accumulation starts from the appropriate identity for the intended model. Complexity claims need the actual operation, container, range and relevant assumptions. A fast average lookup is not a universal constant-time worst-case guarantee. Allocator, iterator validity and exception behavior can matter beyond a simple output trace. These exercises are independent written practice and do not claim that the editorial balance of elementary and advanced items reproduces either credential’s official exam or establishes production performance without measurement.