// Name:    Choi Ka Ho
// No.:     240021155
// Class:   EG114403/1D
// Program: Ex4_Q2

unsigned long previousMillis = 0;

const long interval = 5000;  //5000ms
//Other operations can be performed simultaneously at an interval of
//5000 milliseconds.

void setup() {
  Serial.begin(115600);
}

void loop() {
  unsigned long currentMillis = millis();
  //unsigned byte can represent values from 0 to 255,
  // while signed byte can represent -128 to 127.

  if (currentMillis - previousMillis >= interval) {
    previousMillis = currentMillis;

    for (int k = 9; k > 0; k--) {
      if (k % 2 != 0) { // Odd rows
        for (int j = 1; j <= k; j++) {
          Serial.print(j);
          Serial.print(" ");
        }
      } else { // Even rows
        for (int j = k; j > 0; j--) {
          Serial.print(j);
          Serial.print(" ");
        }
      }
      Serial.println();
    }
  }
}