Got a present for you AA anon.
Where a value, c first appear in row 1 at e for the value a[1], t=1?That is a column e.
Where does it next appear in row 1 at a different e for the value a[t], t=2?
And so on back towards the origin.
Every column that c appears in has what in common?
How many columns do you need to create a lookup?
What specific information does that set of columns build up?
We know a and b are values of n in EVERY one of these columns because c is in the first cell of each column for a value of a[t].
Once you 'c' it, you cannot unsee it.
Godspeed anon.