Zero an arbitrarily large cell in Brainf***
l+r = 0+2 = 2, 55 53 51 bytes

[&gt;+[-&lt;+&gt;&gt;+&lt;]&lt;[&gt;]&gt;[+[-&lt;+&lt;-&gt;&gt;]&lt;[-&gt;+&lt;]]&gt;[-&lt;+&gt;]&lt;&lt;]&gt;[-]&lt;


l+r = 1+2 = 3, 46 44 bytes

[[&gt;+[-&lt;+&lt;+&gt;&gt;]&lt;[&lt;+[-&gt;-&gt;+&lt;&lt;]]&gt;]&gt;[&gt;]&lt;[-]&lt;&lt;[-]&gt;]


My own algorithm. The pointer should begin at the number that needs to be zeroed. The time complexity is O(n^2).

How it works:


We start with the number n.
We increment one, so the number becomes n+1.
We decrement two, so the number becomes n+1-2 = n-1
We increment three, so the number becomes n-1+3 = n+2.
We decrement four, so the number becomes n+2-4 = n-2.


We repeat the process, increasing the in-/decrement each step, until we get zero.