int pins[5] = {D0, D1, D2, D3, D9};

void setup()
{
  // put your setup code here, to run once:
  Serial.begin(115200);
  pinMode(D0, INPUT);

  pinMode(D3, INPUT);
  pinMode(9, INPUT);
}

void probe(int in_pin, int out_pin)
{
  for (int i = 0; i < 5; i++)
  {
    if (i != in_pin && i != out_pin)
    {
      pinMode(pins[i], INPUT);
    }
  }
  pinMode(pins[out_pin], OUTPUT);
  pinMode(pins[in_pin], INPUT_PULLDOWN);
  digitalWrite(pins[out_pin], HIGH);
  delay(5);
  int value = digitalRead(pins[in_pin]);
  if (value == HIGH)
  {
    Serial.print(out_pin);
    Serial.println(in_pin);
  }
}

void loop()
{
  // put your main code here, to run repeatedly:
  for (int out = 0; out < 5; out++)
  {
    for (int in = 0; in < 5; in++)
    {
      if (out != in)
      {
        probe(out, in);
      }
    }
  }

  delay(10);
}