use v6;

my @a = 10, 5, 7, 6, 1;
# my @a = 10;
# my @a = [];

# First approach

my @result;
for @a.reverse.rotor(2 => -1) -> ($a, $b) {
	FIRST @result.push($a);
	state $drop = 0;
	$drop += ($b + 1 - $a) max 0;
	@result.push($b - $drop);
};
say @result ?? @result.reverse !! @a.List;

# Second approach

my @diffs = [\+] @a.reverse.rotor(2 => -1).map: -> ($a, $b) { ($b + 1 - $a) max 0 };
say !@diffs ?? @a.List !! (@a.reverse Z- (0, |@diffs)).reverse;