Question

How to convert a 2D vector to a 1D vector in C++

Answer 1

#include <iostream>
#include <vector>

std::vector<int> arr2DTo1D(const std::vector<std::vector<int>>& arr2d) {
    std::vector<int> arr(arr2d.size() * arr2d[0].size());
    int k = 0;
    
    for (size_t i = 0; i < arr2d.size(); i++) {
        for (size_t j = 0; j < arr2d[i].size(); j++) {
            arr[k++] = arr2d[i][j];
        }
    }
    
    return arr;
}

int main() {
    std::vector<std::vector<int>> arr2d = { 
            { 5, 6, 1 }, 
            { 3, 8, 0 },
            { 9, 2, 7 } 
    };

    std::vector<int> arr = arr2DTo1D(arr2d);

    for (int n : arr) {
        std::cout << n << "\t";
    }
}


 
/*
run:
 
5	6	1	3	8	0	9	2	7
 
*/

 

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Answer 2

#include <algorithm>
#include <iostream>
#include <vector>

int main() {
    std::vector<std::vector<int>> arr2d = { 
            { 5, 6, 1 }, 
            { 3, 8, 0 },
            { 9, 2, 7 } 
    };
 
    std::vector<int> arr;

    for (const auto& row : arr2d) {
        arr.insert(arr.end(), row.begin(), row.end());
    }
 
    for (int n : arr) {
        std::cout << n << "\t";
    }
}
 
 
  
/*
run:
  
5	6	1	3	8	0	9	2	7
  
*/

 

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