C++ Matrix to dynamic 2D arrray (with strings) - c++

Question

Let's say we have a .txt file with data like this:
6
Paris New_York 1
London Berlin 1
Moskow Kiev 1
Paris London 1
New_York Moscow 1
Where 6 is number of Citys and than it means Paris and New_York are connected with value 1, it will always be 1.
Now i would like to turn this into 2D dynamic array. I did it with numbers like this, but i don't know how should i do this with strings.
For numbers:
ifstream myfile("info.txt");
if (myfile.is_open()) {
getline(myfile, line);
istringstream(line) >> Number;
}
int **matrix= new int*[Number];
for (int i = 0; i < Number; i++) {
matrix[i] = new int[Number];
}
while (getline(myfile, line)) {
cout << line << '\n';
std::stringstream linestream(line);
int row;
int column;
int value;
if (linestream >> row >> column >> value)
{
a[row-1][column-1] = value;
a[column-1][row-1] = value;// mirror
}
So how can i do this for strings?
Thank you for your helpful answers

Answer 1

You need an unordered_map<string, int>, beside the matrix, to map string to indexes. Here is my solution:
#include <iostream>
#include <sstream>
#include <string>
#include <fstream>
#include <unordered_map>
using namespace std;
int main() {
string line;
int Number;
ifstream myfile("info.txt");
if (myfile.is_open()) {
getline(myfile, line);
istringstream(line) >> Number;
}
int **matrix= new int*[Number];
for (int i = 0; i < Number; i++) {
matrix[i] = new int[Number](); // note () at the end for initialization to 0
}
unordered_map<string, int> citiesMap; // to map cities (string) to indexes (int)
int cityIndex = 0;
while (getline(myfile, line)){
std::stringstream linestream(line);
string row;
string column;
int value;
if (linestream >> row >> column >> value) {
if(citiesMap.find(row) == citiesMap.cend())
citiesMap[row] = cityIndex++; // add city to the map if it doesn't exist
if(citiesMap.find(column) == citiesMap.cend())
citiesMap[column] = cityIndex++; // add city to the map if it doesn't exist
matrix[citiesMap[row]][citiesMap[column]] = value;
matrix[citiesMap[column]][citiesMap[row]] = value;// mirror
}
}
for(auto x: citiesMap) {
cout << x.first << ": " << x.second << endl;
}
cout << endl;
for(int i = 0; i < Number; i++) {
for(int j = 0; j < Number; j++) {
cout << matrix[i][j] << " ";
}
cout << endl;
}
// matrix should be freed here
}
You may optionally keep unique cities in a vector (or array) to access cities from their indexes. Don't forget to free the memory. Also, you may use std::array for the matrix and don't bother with memory issues.