Before revision: In some puzzles, the strategy we need to use near the goal can be quite different from the strategy that is effective earlier on , e.g. due to a smaller branching factor near the exit state in a maze. A common approach in these casesis to apply both a forward and a backward search, and to try and align the two .
After revision: In some puzzles, the strategy we need to use near the goal can be quite different from the strategy that is effective earlier on , e.g. given only at task completion, remain quite challenging. In such cases, it can be beneficial to tackle the task both from its beginning and end, and make the two ends meet. Existing approaches that do so, however, are not effective in the common scenario where the strategy needed near the end goal is very different from the one that is effective earlier on.