int ledPin[] = {13, 12, 11,10};           // LED pins: MSB to LSB
int ledDelay[4]={8000, 4000,2000, 1000}; // Toggle intervals in milliseconds
// declare other required variables
unsigned long lastChangeTime[4];       // Stores last toggle time for each LED
bool ledState[4];                     // Current state of each LED (HIGH or LOW)
unsigned long currTime;              // Current time tracker

void setup() {
  currTime = millis(); // Initialize current time
  for(int i=0; i<4; i++){
    lastChangeTime[i] = currTime;            // initialize lastChangeTimes
    pinMode(ledPin[i], OUTPUT);              // Set LED pins as OUTPUT
    ledState[i] = LOW;                       // Start with LED OFF
    digitalWrite(ledPin[i], ledState[i]);    // Apply initial state
    
  }
}


void loop() {
  currTime = millis();  // Update current time
  for (int i = 0; i < 4; i++) {
    if (currTime - lastChangeTime[i] >= ledDelay[i]) {
        // Time to toggle this LED
    ledState[i] = !ledState[i];            // Flip state
    digitalWrite(ledPin[i], ledState[i]); // Apply new state
    lastChangeTime[i] = currTime;         // Update last change time
    }
  }
}