Today we will read on this article – Random flip matrix in C ++: If we have n_rows the number of rows and the number of columns of n_cols. All values ​​here are initially 0. We have to define a function flip () that randomly selects the 0 value equally, changes it to 1, and then returns the position of that value to [row.id, col.id]. In addition, we need to write another function reset (), which sets all values ​​to 0.. We need to reduce the number of calls to Math.random () of the system and try to optimize the complexity of time and space.

Example

#include <bits/stdc++.h>
using namespace std;
void print_vector(vector<int> v){
   cout << "[";
   for(int i = 0; i<v.size(); i++){
      cout << v[i] << ", ";
   }
   cout << "]"<<endl;
}
class Solution {
   public:
   unordered_map <int, int> holes;
   int n;
   int m;
   int size;
   program(int n_rows, int n_cols) {
      srand(time(NULL));
      n = n_rows;
      m = n_cols;
      size = n * m;
   }
   vector<int> flip() {
      int id = rand() % size;
      size--;
      int rid = id;
      if(holes.count(id)){
         id = holes[id];
      }
      holes[rid] = holes.count(size) ? holes[size] : size;
      return {id / m, id % m};
   }
   void reset() {
      size = n * m;
      holes.clear();
   }
};
main(){
   Solution ob(2,2);
   print_vector(ob.flip());
   print_vector(ob.flip());
   print_vector(ob.flip());
   print_vector(ob.flip());
}

Input

Initialize the constructor using 2,2 and call flip four times

Output

[1, 1, ]
[0, 0, ]
[1, 0, ]
[0, 1, ]