block avoidance algo help

Hi all,
i am participating in a competition where my autonomous bot have to differentiate between two types of block(essentially placed on the intersections of a grid) & deposit one of them at target position, avoiding contact with other type of block. sensors will take care of differentiating the blocks.
The problem is that if the bot follows scanning columnwise (or rowwise) & detect obstacle block in path, how should bot go about modifying the path dynamically. any standard algorithm which comes to help in such problems? elaborate explanation with pseudocode is most welcome.

Do you know where your block is beforehand or not? Can your robot know where in the grid it is at any point?