# define N 13  // # to shuffle 1 .. N

byte array[N];

char buffer[80];

void setup() {
  Serial.begin(115200);
  Serial.println("\hi Mom!");

  pinMode(2, INPUT_PULLUP);

  randomSeed(0xb4dc0de);

// init once only

  for (byte ii = 0; ii < N; ii++) array[ii] = N - 1 - ii;  // just for fun

  printArray();
}

void loop() {
  topInAtRandom();
  printArray();

  delay(300);
  while (digitalRead(2) == HIGH);
}

void topInAtRandom()
{
  int iterations = 0;

  byte peek = array[0];     // stop when the botton card gets to the top
  while (array[N - 1] != peek) {
    iterations++;

    byte card = array[N - 1];     // the top card
    byte into = random(0, N);     // in at random spot [0, N)

    if (1) {
      snprintf(buffer, 79, "top card %c goes in at %2d. -> ", 'A' + card, into);
      Serial.print(buffer);
    }

// move cards up, freeing the into slot
    for (byte ii = N - 1; ii > into; ii--)
      array[ii] = array[ii - 1];

// put that top card in the random slot
    array[into] = card;

    if (1) printArray();
  }

  snprintf(buffer, 79, "\niterations = %d\n", iterations);
  Serial.print(buffer);
}

void printArray()
{
  for (byte ii = 0; ii < N; ii++) {
    snprintf(buffer, 79, "%c ", 'A' + array[ii]);
    Serial.print(buffer);
  }

  Serial.println("");
}