C++中具有用户定义大小的2D矢量vector

2021年3月9日16:17:36 发表评论 799 次浏览

本文概述

2D向量是

向量

向量。像2D数组一样, 我们可以声明值并将其分配给2D向量！

假设你熟悉C ++中的法向矢量, 在一个示例的帮助下, 我们演示了2D向量与以下法向矢量的不同之处：

CPP

// CPP program
#include <iostream>
 
/* Vectors belong to a C++ library
    called STL so we need to import
    it first! */
#include <vector>
using namespace std;
int main()
{
     /*
     In the case of a normal vector we initialize it as:
     
     1. vector<datatype> variable_name
     
     Now in the case of a 2D vector all we do is create
     a vector of datatype vector.
     
     We simply replace "datatype" with "vector<int>":
     
     1. vector<vector<int>> variable_name
     
     That's literally it! We just created a 2D vector!
     On line 23 below we declare an actual 2D vector
     named "vect".
     */
     
     vector<vector< int >> vect;
 
     return 0;
}

在2D向量中, 每个元素都是一个向量。

CPP

/* C++ code to demonstrate a 2D vector
    with elements(vectors) inside it. */
#include <iostream>
#include <vector>
using namespace std;
 
int main()
{
     /*
     Below we initialize a 2D vector
     named "vect" on line 12 and then
     we declare the values on
     line 14, 15 and 16 respectively.
     */
     
     vector<vector< int >> vect
     {
         {1, 2, 3}, {4, 5, 6}, {7, 8, 9}
     };
     
     /*
     Now we print the values that
     we just declared on lines
     14, 15 and 16 using a simple
     nested for loop.
     */
     
     for ( int i = 0; i < vect.size(); i++)
     {
         for ( int j = 0; j < vect[i].size(); j++)
         {
             cout << vect[i][j] << " " ;
         }   
         cout << endl;
     }
 
     return 0;
}

输出：

1 2 3 
4 5 6 
7 8 9

喜欢Java的锯齿状数组, 二维向量的每个元素可以包含不同数量的值。

CPP

/*
C++ program to demonstrate a 2D vector where
each of its elements is of different size.
*/
#include <iostream>
#include <vector>
using namespace std;
int main()
{
     /*
     We initialize a 2D vector
     named "vect" on line 16 with
     different number of values
     in each element.
     */
     
     vector<vector< int >> vect
     {
         /* Element one with 2 values in it. */
         {1, 2}, /* Element two with 3 values in it. */
         {4, 5, 6}, /* Element three with 4 values in it. */
         {7, 8, 9, 10}
     };
 
     /*
     Now we print the vector that we
     just defined using a simple
     nested for loop.
     */
     
     for ( int i = 0; i < vect.size(); i++)
     {
         for ( int j = 0; j < vect[i].size(); j++)
         {
             cout << vect[i][j] << " " ;
         }   
         cout << endl;
     }
     return 0;
}

输出：

1 2 
4 5 6 
7 8 9 10

运动题：

用不同大小的列定义2D向量。

例子：

Input : Number of rows : 5 
        Number of columns in rows : 
        2 3 4 5 1
Output : 1 2
         1 2 3
         1 2 3 4
         1 2 3 4 5 
         1

Input : Number of rows : 3
        Number of columns in rows : 
        3 2 1

Output : 1 2 3
         1 2
         1

2D向量通常被视为内部带有"行"和"列"的矩阵。实际上, 它们实际上是2D矢量的元素。

我们首先声明一个名为" row"的整数变量, 然后声明一个名为" column"的数组, 该数组将保存每行大小的值。

之后, 我们将根据列的大小来初始化每一行的内存。

CPP

/*
C++ program to create a 2D vector where
every row has a certain number of values
as defined by the user.(On line 13)
*/  
 
#include <iostream>
#include <vector>
using namespace std;
int main()
{
     
     /* Here we tell how many rows
     the 2D vector is going to have. */
     int row = 5;
   
     /* We define the number of values
     each row is supposed to have. */
     int colom[] = {5, 3, 4, 2, 1};
 
     /*
     We now create a vector of vector with size
     equal to row.
     */
     
     vector<vector< int >> vec(row);
     /*
     On line 21 we created a 2D vector and assinged
     it a capacity of "row"(in this case 5) units.
     */
     
     /*
     Now we will proceed to create the sturture of
     our 2D vector by assigning the value of rows and
     columns through a nested for loop.
     */
 
     for ( int i = 0; i < row; i++)
     {  
         /* Declaring the size of the column. */
         int col = colom[i];
 
         /*
         On the 43rd line we declare the
         i-th row to the size of the column.
         We create a normal vector of capacity "col" which
         in every iteration of the for loop will define the
         values inside of each row.
         */
         vec[i] = vector< int >(col);
         for ( int j = 0; j < col; j++)
         {
             vec[i][j] = j + 1;
         }   
     }
     
     /*
     We now finally use a simple nested for loop
     to print the 2D vector that we just created above.
     */
 
     for ( int i = 0; i < row; i++)
     {
         for ( int j = 0; j < vec[i].size(); j++)
         {
             cout << vec[i][j] << " " ;
         }   
         cout << endl;
     }
     return 0;
}

输出如下：

另一种方法

假设我们要初始化一个2D向量

" n"

行和

" m"

列, 值为0。

CPP

// CPP program
#include <iostream>
#include <vector>
using namespace std;
int main()
{
     int n = 3;
     int m = 4;
 
     /*
     We create a 2D vector containing "n"
     elements each having the value "vector<int> (m, 0)".
     "vector<int> (m, 0)" means a vector having "m"
     elements each of value "0".
     Here these elements are vectors.
     */
     vector<vector< int >> vec( n , vector< int > (m, 0));
 
     for ( int i = 0; i < n; i++)
     {
         for ( int j = 0; j < m; j++)
         {
             cout << vec[i][j] << " " ;
         }
         cout<< endl;
     }
     
     return 0;
}

输出如下：

0 0 0 0 
0 0 0 0
0 0 0 0

另一种方法：

假设我们要创建一个2D向量

" n"

行和

" b"

列和输入值。

CPP

// CPP program
#include <iostream>
#include <vector>
using namespace std;
int main()
{
     int n = 4;
     int m = 5;
 
     /*
     Create a vector containing "n"
     vectors each of size "m".
     */
     vector<vector< int >> vec( n , vector< int > (m));
 
     for ( int i = 0; i < n; i++)
     {
         for ( int j = 0; j < m; j++)
         {
             vec[i][j] = j + i + 1;
         }
     }
 
     for ( int i = 0; i < n; i++)
     {
         for ( int j = 0; j < m; j++)
         {
             cout << vec[i][j] << " " ;
         }
         cout << endl;
     }
     
    return 0;
}

输出如下：