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Lecture 17—Search Problems 2

Before Lecture

Before this lecture you need to watch the Sudoku videos in module 9b carefully. We are saying watch carefully not work through, but emphasis on the carefully.

During Lecture

The starters for this lecture are:

After Lecture

Again, search programs build on every single thing we've learned so far except HtDW! HtDD, HtDF, atomic data, compound data, lists, trees, backtracking, generative recursion — all of it! These are truly excellent problems to practice what you have learned so far in the course, and even if they are difficult for you they are excellent problems to feel good about how much you have learned.

To review today's material:

Once again, redo the template blending of arbitrary arity tree and generative recursion and backtracking search from scratch and write out the wishlist entries.
Write the termination argument for the main function.
Then complete the wishlist entries.
You can also review this material by working slowly through the Sudoku videos.

Here is one more example if you want even more practice. NQueens is simpler than triangle solitaire because the board geometry of triangle solitaire is a bit complicated. But the core of each problem is the same - a backtracking search over a generated arbitrary-arity tree.

nqueens-starter.rkt	Just has the problem statement.
nqueens-v1.rkt	Also has data definitions, the start of the main search function, and a useful helper.
nqueens-v2.rkt	Also has the arb-tree template.
nqueens-solution.rkt	Complete solution.

The solution for this lecture is:

m09-search-triangle-solitaire-solution.rkt

Be sure to complete the before lecture section of Lecture 18 before that lecture.