filled color effect cylon

hi… need help…please help…

i do learning a lot about arduino… most all in lightning… iam new with fastled. i play with nano n led ws2812 and use fastled library…

what i want is how to make effect like filled water empty glass… example with larson scanner/chaser.

for (int i = 0; i<NUM_LEDS; i++){
leds[i]=CRGB::Red;
FastLED.show();
leds[i]=CRGB::Black;
delay(50);

from that code above assum use 5 led, how to make led start running and stop at led 5 n lit up n loop again n stop at led 4 n lit up…

i want every led stop the led lit up even led start loop again from first led.

it like this :
10000 01000 00100 00010 00001 10001 01001 00101 00011 10011 01011 00111 10111 01111 11111

for (int i = firstLED; i<lastLED; i++){

Is the way you restrict any effect you apply to only a section of the LEDs in a strip.