C++ STL 中的集合数组

数组是存储在连续内存位置的项目的集合。它是将多个相同类型的项目存储在一起。这使得通过每个元素的位置访问存储在其中的元素变得更加容易。

集合是一种关联容器，其中每个元素都必须是唯一的，因为元素的值可以标识它。元素的值一旦添加到集合中就无法修改，但可以删除和添加该元素的修改后的值。

因此，集合数组是具有固定行数的二维数组，其中每行是一组可变长度。数组的每个索引存储一个可以使用迭代器遍历和访问的集合。

句法：

set S[size];

例子：

set< int >S[5], where S is the array of sets of int of size 5

在集合数组中插入：使用 insert()函数在每个集合中插入元素。下面是演示在集合数组中插入操作的示例：

C++

// C++ program to demonstrate the
// insertion in the array of sets
#include 
using namespace std;
#define ROW 4
#define COL 5
  
// Driver Code
int main()
{
    // Declaring array of sets
    set s[ROW];
  
    // Elements to insert
    // in set
    int num = 10;
  
    // Inserting elements
    // into sets
    for (int i = 0; i < ROW; i++) {
        // Insert the column elements
        for (int j = 0; j < COL; j++) {
            s[i].insert(num);
            num += 5;
        }
    }
  
    // Display the array of sets
    for (int i = 0; i < ROW; i++) {
        cout << "Elements at index " << i << ": ";
  
        // Print the array of sets
        for (auto x : s[i])
            cout << x << " ";
  
        cout << endl;
    }
  
    return 0;
}

输出：

Elements at index 0: 10 15 20 25 30 
Elements at index 1: 35 40 45 50 55 
Elements at index 2: 60 65 70 75 80 
Elements at index 3: 85 90 95 100 105

删除集合数组中的元素：从每个集合中删除元素是使用erase()函数的。下面是一个例子来演示集合数组中的删除操作：

C++

// C++ program to demonstrate the
// deletion in the array of sets
#include 
using namespace std;
  
// Defining the length of array
// and number of elements in
// each set
#define ROW 4
#define COL 5
  
// Driver Code
int main()
{
    // Declaring array of sets
    set s[ROW];
    int num = 10;
  
    // Inserting elements in the set
    // at each index of array
    for (int i = 0; i < ROW; i++) {
  
        // insert the column elements
        for (int j = 0; j < COL; j++) {
            s[i].insert(num);
            num += 5;
        }
    }
  
    cout << "Before removal elements are:"
         << endl;
  
    // Display the array of sets
    for (int i = 0; i < ROW; i++) {
        cout << "Elements at index "
             << i << ": ";
        for (auto x : s[i])
            cout << x << " ";
        cout << endl;
    }
  
    // Erase 70 from 3rd set
    s[2].erase(70);
  
    // Erase 55 from 2nd set
    s[1].erase(55);
  
    // Display the array of sets
    // after removal of elements
    cout << endl
         << "After removal elements are:"
         << endl;
  
    for (int i = 0; i < ROW; i++) {
        cout << "Elements at index "
             << i << ": ";
  
        // Print the current set
        for (auto x : s[i])
            cout << x << " ";
  
        cout << endl;
    }
  
    return 0;
}

输出：

Before removal elements are:
Elements at index 0: 10 15 20 25 30 
Elements at index 1: 35 40 45 50 55 
Elements at index 2: 60 65 70 75 80 
Elements at index 3: 85 90 95 100 105 

After removal elements are:
Elements at index 0: 10 15 20 25 30 
Elements at index 1: 35 40 45 50 
Elements at index 2: 60 65 75 80 
Elements at index 3: 85 90 95 100 105

集合数组中的遍历：在 array[index] 的帮助下从集合数组中遍历每个集合，并使用迭代器执行集合中的遍历。下面是说明在集合数组中遍历的程序：

C++

// C++ program to demonstrate the
// traversal in the array of sets
#include 
using namespace std;
#define ROW 2
  
// Driver Code
int main()
{
    // Declaring array of sets
    set s[ROW];
  
    // Inserting elements into sets
    // Insert 10, 15, and 35 in 1st set
    s[0].insert(10);
    s[0].insert(15);
    s[0].insert(35);
  
    // Insert 20 and 30 in 2nd set
    s[1].insert(20);
    s[1].insert(30);
  
    // Traversing of sets s to print
    // elements stored in it
    for (int i = 0; i < ROW; i++) {
        cout << "Elements at index "
             << i << ": ";
  
        // Traversing and printing
        // element  at each column,
        // begin() is the starting
        // iterator, end() is the
        // ending iterator
        for (auto it = s[i].begin();
             it != s[i].end();
             it++) {
  
            // (*it) is used to get the
            // value at iterator is pointing
            cout << *it << ' ';
        }
  
        cout << endl;
    }
  
    return 0;
}

输出：

Elements at index 0: 10 15 35 
Elements at index 1: 20 30

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