How to calculate the upper-layer number of such a topology?-php Tutorial

How can I calculate the numbers on the upper layer, and each layer has two nodes? now, how can I know that the upper layer of 8 has 1, 2, and 4?
How can we calculate 1, 2, and 5 on 10?

Sincerely ask for advice!

Reply to discussion (solution)

Each number records its parent
The parent level of 1 is 0.
The parent level of 2 and 3 is 1.
4. the parent class of 5 is 2, 6, and 7 is 3.
And so on

Then recursively look for a number of parent levels until the parent level is 0.

Complete binary tree

$ N = 10 ;//
While ($ n> 1 ){
$ N = floor ($ n/2 );
Echo $ n ."";
}
?>

Let's take a look at the binary tree section of the data structure.