N X M * M X L = N X L
3중 for문 사용
#include <string>
#include <vector>
using namespace std;
vector<vector<int>> solution(vector<vector<int>> arr1, vector<vector<int>> arr2) {
int n = arr1.size();
int m = arr2.size();
int l = arr2[0].size();
// N X L 크기 행렬, 0 초기화
vector<vector<int>> answer(n, vector<int>(l,0));
for(int i = 0; i < n ; i++){
for(int j = 0; j < l; j++){
for(int k = 0; k < m; k++){
answer[i][j] += arr1[i][k] * arr2[k][j];
}
}
}
return answer;
}