I want to ask about 2d vectors

CodeChef-DSA-learners
1

how initialize 2d vector for user define data i am facing a problem while doing so here is my code

int main() {
int t;
cin>>t;
while(t–){
int N,M,a;
cin>>N>>M;
vector < vector < int >> arr;
for(int i=0;i<N;i++)
{
for(int j =0;j<M;j++){
cin>>a;
arr.push_back(a);
}
}

setZeroes(arr);
cout<<"The Final Matrix is "<<endl;
for (int i = 0; i < arr.size(); i++) {
for (int j = 0; j < arr[0].size(); j++) {
cout << arr[i][j] << " ";
}
cout << “\n”;
}
return 0;
}

I have define this function to find the zero’s element from the ith row and jth col. but what I am doing wrong here plz… can anyone tell ,me what I am mistaking here

2

Your First doubt :- You can initialize 2-D vectors as :-

vector < vector < int > > your_Vector_Name(row_Size, vector < int > (column_size, your_Data) )

For ex :-
vector < vector < int > > firstVec(20, vector < int > (10, 0) )

will create a 20 x 10 matrix of values 0 assigned.

Your second doubt about the code :- you cann’t push_back an int to a vector<vector>. You have to push_back a vector of int.

So code should look like :-

   for(int i=0;i<N;i++)
  {
     vector<int> tempV;
     for(int j =0;j<M;j++){
        cin>>a;
        tempV.push_back(a);
     }
     arr.push_back(tempV);
}
1 Like
3

Thank u for replying i have cried a diffrent way instead of making another vector i took my 2d vector then .initials 2 for looks and what i have dine that my vectors name was arr so i took arr[i][j]=a;
And a is the variables i used to take input from the user is this right approach