使用递归将元素添加到矢量中

Question

我有一个二维矢量，我反复添加元素。我知道如何使用嵌套for循环来做到这一点。但是，我想知道是否有一种方法来使用递归？这里是我使用循环的代码：

#include <vector> 
#include <iomanip> 
#include <iostream> 

using std::cin; 
using std::cout; 
using std::endl; 
using std::setw; 
using std::vector; 

int main() { 
    vector<vector<int > >test; 
    int items; 
    cout<< "How many items" <<endl; 
    cin>> items; 

    for (int i = 0; i < items+1; i++) { 
     vector<int> row; // Create an empty row 

     for (int j = 0; j < items+1; j++) { 
      row.push_back((i-1)+j); // Add an element(column) to the row 
     } 
     test.push_back(row); 
    } 

    for (int i = 1; i < items+1; i++) { 
     for (int j = 1; j < items+1; j++) { 
      cout << setw(4)<<test[i][j]; 
     } 
     cout << endl; 
    } 
    return 0; 
} 

什么是最有效的方法来把它变成一个递归函数？

Answer 1

这里，

#include "iostream" 
#include "iomanip" 
#include "vector" 
using namespace std; 

void insert (vector < vector <int> >& my_vector, int& items, vector <int>& row, int value, int index) 
{ 
    if (row.size()==items) // check if row is complete 
    { 
     my_vector.push_back(row); // add row to 2D vector 
     row.clear(); 
     if (index<items) 
      insert(my_vector, items, row, index+1, index+1); // for next row 
    } 
    else // row is not complete 
    { 
     row.push_back(value); // add element to row 
     insert(my_vector, items, row, value+1, index); // for next element 
    } 
} 

int main() 
{ 
    int items; 
    cout << "How many items? "; 
    cin >> items; 
    vector < vector <int> > my_vector; 
    vector <int> row; 
    insert(my_vector, items, row, 1, 1); 
    for (auto i: my_vector) 
    { 
     for (auto j: i) 
      cout << setw(4) << j; 
     cout << endl; 
    } 
} 

Answer 2

#include <dirent.h> 
#include <iostream> 
#include <vector> 
#include <string> 

// Programed by Scourge 
// GNU GPLv3 

using std::cout; 
using std::cin; 
using std::endl; 
using std::string; 
using std::vector; 

// This is a good method because we can get all the files (with or without folder) recursive or not 
// from a target directory, and then have all those elements placed into a vector for easy 'for' 
// loop usage and functional parsing. 

vector<string> scan_dir(string scan_start, string scope, string include_folder, vector<string> &vec_track){ 

    DIR *current_dir = opendir (scan_start.c_str()); // starting dir given as a string 

    // "dir_item" can be anything in the "current_dir" such as a new folder, file, binary, etc. 

    while (struct dirent *dir_item_ptr = readdir(current_dir)){ 
     string dir_item = (dir_item_ptr->d_name); // structure points to the getter to retrive the dir_item's name. 
     if (dir_item != "." and dir_item != "./" and dir_item != ".."){ 
      if (dir_item_ptr->d_type == DT_DIR){ 
       if(scope == "r" or scope == "-r"){ 
        if(include_folder == "f" or include_folder == "-f"){ 
         vec_track.push_back(dir_item); 
        } 
        scan_dir(scan_start + "/"+ dir_item, scope, include_folder, vec_track); // recursive function 
       } 
      }else if(dir_item == "read"){ 
       break; // full dir already read, leave the loop 
      }else{ 
       vec_track.push_back(dir_item); 
      } 
     } 
    } 
    return vec_track; 
    closedir (current_dir); 
} 

int main(){ 

    vector<string> rec_vec; 
    vector<string> pwd_vec; 

    // './' as arg 1 sets the target folder to your PWD 

    scan_dir("./","-r","-f", rec_vec); // "scope"   = '-r' = target_folder recursive search 
    // recursive vector from pwd  // "include_folder" = '-f' = include folders in the results 

    scan_dir("./","-n","-n", pwd_vec); // "scope"   = '-n' = use target_folder but not recursive 
    // pwd vector      // "include_folder = '-n' = not folder included 


    for(string& i: rec_vec){cout << i << endl;} // loop through and print the vector's elements 
    cout << "---------------------\n"; 
    for(string& i: pwd_vec){cout << i << endl;} // loop through and print the vector's elements 

    return 0; 
} 

// My Background. . . 
// github.com/Radicalware 
// Radicalware.net 
// https://www.youtube.com/channel/UCivwmYxoOdDT3GmDnD0CfQA/playlists