vector<pair<int, int>> act(number)是什么意思

这行代码定义了一个名为act的变量，其类型为vector<pair<int, int>>，表示一个元素为pair<int, int>类型的动态数组。其中，number为数组的大小，表示act数组中有number个元素。每个pair<int, int>类型的元素包含两个int类型的值，可以理解为一个二元组。

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vector<vector<pair<int,int>>>

This is a vector of vectors, where each element of the outer vector is a vector of pairs of integers.

For example,

vector<vector<pair<int,int>>> v;

creates an empty vector of vectors. To add a vector of pairs to this, we can do:

vector<pair<int,int>> inner; // create an inner vector
inner.push_back(make_pair(1,2)); // add a pair to the inner vector
inner.push_back(make_pair(3,4)); // add another pair to the inner vector
v.push_back(inner); // add the inner vector to the outer vector

Now, `v` contains one vector of pairs:

v = [
    [(1,2), (3,4)]
]

We can add more vectors of pairs to `v` in a similar way.

This data structure is useful for storing a collection of pairs where each pair belongs to a different group or category. For example, if we are storing the grades of students in a class, we can have a vector for each subject and each vector contains pairs of (student_id, grade).

priority_queue<pair<int, int>, vector<pair<int, int>>, greater<pair<int, int>>> pq

This is a declaration of a priority queue in C++ that stores pairs of integers. The priority queue is implemented using a min-heap, which means that the smallest element will have the highest priority. The first integer in the pair is the priority and the second integer is the value.

The syntax for declaring a priority queue in C++ is:

priority_queue<data_type, container_type, comparison_function>

In this case, the data type is a pair of integers (pair<int, int>), the container type is a vector (vector<pair<int, int>>), and the comparison function is the default less-than operator (>).

However, in order to implement a min-heap, we need to use the greater-than operator (<) instead. So we pass greater<pair<int, int>> as the comparison function.

Overall, this priority queue will store pairs of integers in ascending order of their first element. If two pairs have the same first element, then they will be ordered based on their second element in ascending order as well.