怎么向vector<pair<int,int>>中添加元素

有两种方法可以向vector<pair<int,int>>中添加元素：

1. 使用push_back()函数：

vector<pair<int,int>> v; // 定义vector<pair<int,int>>类型的v
int a = 1, b = 2;
v.push_back(make_pair(a, b)); // 向v中添加一个pair<int,int>类型的元素

2. 使用emplace_back()函数：

vector<pair<int,int>> v; // 定义vector<pair<int,int>>类型的v
int a = 1, b = 2;
v.emplace_back(a, b); // 向v中添加一个pair<int,int>类型的元素

注意，以上两种方法都是向vector的末尾添加一个元素，如果要在指定位置添加元素，可以使用insert()函数。

相关问题

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.