Print all combinations of a 3D vector - c++

Question

Suppose I have a vector<vector<vector<int> > > result.
The only size I know before hand is the inner and outer vector, which are of size k.
if I print result I get this (for k = 3):
i = 0
0 1 2
3 4 5
i = 1
6 7 8
9 10 11
12 13 14
i = 2
15 16 17
18 19 20
What I need to do is to print every combinations of k rows from each of vector of vectors of i's. In other words, what I need is the following output:
0 1 2
6 7 8
15 16 17
0 1 2
6 7 8
18 19 20
0 1 2
9 10 11
15 16 17
...
3 4 5
12 13 14
18 19 20
Hope I was clear about the desired output. I have tried a thousand of different loops, trying to save in another vector<vector<int> > but no success so far. I really am lost and any help would be greatly appreaciated.
The code to generate the above output is here:
(I'm sorry, I know it is an ugly code but it was the closest I could get to demonstrate my problem in a MCVE code)
#include <iostream>
#include <vector>
using namespace std;
int main(){
vector<vector<vector<int> > > result;
int k = 3;
vector<vector<int> > randomVectors;
//I'll create seven random vectors
//In my original problem, I don't have this number beforehand
int number = 0;
for(int i = 0; i < 7; i++){
vector<int> temp;
for(int j = 0; j < k; j++){
temp.push_back(number);
number++;
}
randomVectors.push_back(temp);
}
//Vector of vector to assign to "result"
vector<vector<int> > randomVectors_0;
randomVectors_0.push_back(randomVectors[0]);
randomVectors_0.push_back(randomVectors[1]);
vector<vector<int> > randomVectors_1;
randomVectors_1.push_back(randomVectors[2]);
randomVectors_1.push_back(randomVectors[3]);
randomVectors_1.push_back(randomVectors[4]);
vector<vector<int> > randomVectors_2;
randomVectors_2.push_back(randomVectors[5]);
randomVectors_2.push_back(randomVectors[6]);
result.push_back(randomVectors_0);
result.push_back(randomVectors_1);
result.push_back(randomVectors_2);
cout << "Printing the 3D vector" << endl;
for(int i = 0; i < k; i++){
cout << "i = " << i << endl << endl;
for(int j = 0; j < result[i].size(); j++){
for(int m = 0; m < k; m++){
cout << result[i][j][m] << " ";
}
cout << endl;
}
cout << endl;
}
return 0;
}
Compiler version: gcc (tdm-1) 4.7.1

Answer 1

I would make a rows_to_print vector that starts with all 0's. Then once a loop, it'll increment the last value by 1. If that value is greater than the size of the last vector, then reset it to 0 and increment the next value up the list, etc... you're done looping when every value in rows_to_print is greater than the size of each of the vectors:
void print_rows(std::vector<size_t> rows, std::vector<std::vector<std::vector<int>>> v) {
for(size_t x = 0; x < v.size(); x++) {
for(size_t y = 0; y < v.at(x).at(rows.at(x)).size(); y++) {
std::cout << v.at(x).at(rows.at(x)).at(y) << ' ';
}
std::cout << std::endl;
}
}
bool increment_rows(std::vector<size_t> &rows, std::vector<std::vector<std::vector<int>>> v) {
if(!rows.size()) return false; //empty rows, BAD
rows.at(rows.size() - 1)++;
for(int x = rows.size() - 1; x >= 0; x--) {
if(rows.at(x) >= v.at(x).size()) {
if(x <= 0) { return false; } //first row is done, then we're done!
rows.at(x-1)++; //increment previous row and set us back to 0 (overflow)
rows.at(x) %= v.at(x).size();
}
}
return true;
}
int main() {
...
std::vector<size_t> rows_to_print(k, 0);
print_rows(rows_to_print, result);
while(increment_rows(rows_to_print, result)) {
print_rows(rows_to_print, result);
}
}
See it in action here: ideone