Hello there! In this unit, we're offering an engaging coding lesson that highlights the performance efficiencies offered by the utilization of std::unordered_map in C++. We'll address a vector-based problem that requires us to make an optimal choice to minimize the size of our vector. Excited? So am I! Let's get started.

In this unit's task, we'll manipulate a vector of integers. You are required to construct a C++ function titled minimal_max_block(). This function should accept a vector as an input and compute an intriguing property related to contiguous blocks within the vector.

More specifically, you must select a particular integer, k, from the vector. Once you've selected k, the function should remove all occurrences of k from the vector, thereby splitting it into several contiguous blocks or remaining sub-vectors. A unique feature of k is that it is chosen such that the maximum length among these blocks is minimized.

For instance, consider the vector {1, 2, 2, 3, 1, 4, 4, 4, 1, 2, 5}. If we eliminate all instances of 2 (our k), the remaining blocks would be {1}, {3, 1, 4, 4, 4, 1}, , with the longest containing 6 elements. Now, if we instead remove all instances of 1, the new remaining blocks would be , , , the longest of which contains 3 elements. As such, the function should return 1 in this case, as it leads to a minimally maximal block length.