I'm not sure what the best way to do draw this on SO, but basically, you want to compare adjacent cells and increment if same and reset to 1 if not, right?

A1: "Apple"          B1: 1
A2: "Apple"          B2: =if(A2=A1, B1+1, 1)
A3: "Apple"          B3: =if(A3=A2, B2+1, 1)
(and so on)