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Give a recursive algorithm for tiling a \(2^{n} \times 2^{n}\) checkerboard with one square missing using right triominoes.

Short Answer

Expert verified
Divide the \(2^n \times 2^n\) board into four \(2^{n-1} \times 2^{n-1}\) sub-boards, place a triomino at the center, then recursively tile the smaller boards.

Step by step solution

01

Understand the Problem

The exercise requires filling a checkerboard of size \(2^n \times 2^n\), which has one square missing, using L-shaped tiles called triominoes. These triominoes can cover exactly 3 squares each.
02

Base Case

For the smallest checkerboard size \(2^1 \times 2^1\) (i.e., a 2x2 board), if one square is missing, the remaining squares can be covered with one triomino.
03

Divide the Checkerboard

Divide the \(2^n \times 2^n\) board into four smaller \(2^{n-1} \times 2^{n-1}\) sub-boards. Identify the sub-board containing the missing square. Place one triomino at the center to cover the center squares of the three sub-boards not containing the missing square.
04

Apply Recursion

Recursively tile the four \(2^{n-1} \times 2^{n-1}\) boards, treating the placement of the central triomino as creating a new 'missing square' for three of the boards.
05

Combine the Solutions

After the recursive step finishes tiling each \(2^{n-1} \times 2^{n-1}\) sub-board, the entire \(2^n \times 2^n\) board is completed.
06

Formalize the Recursive Algorithm

Define the recursive algorithm as follows:1. Base case: If the size of the board is \(2 \times 2\), place one triomino to cover the three non-missing squares.2. Recursive step: Otherwise, divide the board into four \(2^{n-1} \times 2^{n-1}\) sub-boards. Place a triomino at the center to cover the central squares of the three sub-boards without the missing square. Recursively tile each \(2^{n-1} \times 2^{n-1}\) sub-board.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

recursion
Recursion is a fundamental concept in computer science and mathematics. It involves solving a problem by breaking it down into smaller sub-problems that are similar to the original problem. A function is said to be recursive if it calls itself within its definition.

For example, in the checkerboard tiling problem, the recursive algorithm breaks the large board into smaller boards and solves each one of them in a similar manner. This continues until the problem is reduced to a simple, easily solvable case, known as the base case.
triomino tiling
A triomino is an L-shaped tile that covers exactly three squares of a checkerboard. In the context of the given problem, we are asked to tile a checkerboard of size \(2^n \times 2^n\) with one square missing, using these triominoes.

The triomino can be rotated in four different ways, but it will always cover three contiguous squares in an L-shape. The key to solving the problem is to strategically place the triominoes so that the entire board gets covered except for the initially missing square. The triominoes help divide the problem into more manageable sub-problems, facilitating a recursive solution.
divide and conquer algorithm
Divide and conquer is a powerful algorithmic strategy where a problem is divided into smaller sub-problems that are easier to handle. Each sub-problem is solved independently, and their solutions are combined to form the solution of the original problem.

In the checkerboard tiling problem, the board is divided into four smaller boards. The missing tile creates a natural division point. A triomino is placed at the center to cover parts of the sub-boards not containing the missing square, making the problem smaller and more manageable. The recursive application of this approach leads to the complete tiling of the checkerboard.
base case
The base case is the simplest instance of a problem, which can be solved directly without further recursion. It acts as the termination condition for a recursive algorithm.

In the checkerboard tiling problem, the base case occurs when the board size is \(2 \times 2\), the smallest size that fits our recursive pattern. With one square missing, the remaining three squares can be covered perfectly by one triomino. Identifying and correctly implementing the base case ensures that the recursion process terminates properly and the overall solution is correct.
checkerboard problem
The checkerboard problem involves tiling a board of size \(2^n \times 2^n\) with one square missing using L-shaped triominoes. This is a classic problem that combines several important concepts in algorithm design, such as recursion and divide and conquer.

The challenge is to cover the board completely except for the one missing square. This requires strategic placement of the triominoes and careful management of the missing square's location throughout the recursive process. By dividing the board into smaller sub-boards and solving each one recursively, the problem can be managed efficiently, demonstrating the power of these algorithmic concepts.

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Most popular questions from this chapter

Use the well-ordering property to show that if \(x\) and \(y\) are real numbers with \(x1 /(y-x)\) . Then show that there is a rational number \(r\) with denominator \(A\) between \(x\) and \(y\) by looking at the numbers \(\lfloor x\rfloor+ j / A,\) where \(j\) is a positive integer.]

Determine whether each of these proposed definitions is a valid recursive definition of a function \(f\) from the set of nonnegative integers to the set of integers. If \(f\) is well defined, find a formula for \(f(n)\) when \(n\) is a nonnegative integer and prove that your formula is valid. a) \(f(0)=0, f(n)=2 f(n-2)\) for \(n \geq 1\) b) \(f(0)=1, f(n)=f(n-1)-1\) for \(n \geq 1\) c) \(f(0)=2, f(1)=3, f(n)=f(n-1)-1\) for \(n \geq 2\) d) \(f(0)=1, f(1)=2, f(n)=2 f(n-2)\) for \(n \geq 2\) e) \(f(0)=1, f(n)=3 f(n-1)\) if \(n\) is odd and \(n \geq 1\) and \(\quad f(n)=9 f(n-2)\) if \(n\) is even and \(n \geq 2\)

Let \(S\) be the subset of the set of ordered pairs of integers defined recursively by Basis step: \((0,0) \in S\) . Recursive step: If \((a, b) \in S,\) then \((a, b+1) \in S\) \((a+1, b+1) \in S,\) and \((a+2, b+1) \in S\) a) List the elements of \(S\) produced by the first four ap- plications of the recursive definition. b) Use strong induction on the number of applications of the recursive step of the definition to show that \(a \leq 2 b\) whenever \((a, b) \in S .\) c) Use structural induction to show that \(a \leq 2 b\) whenever \((a, b) \in S .\)

In Exercises 29 and \(30, H_{n}\) denotes the \(n\) th harmonic number. Prove that \(H_{2^{n}} \leq 1+n\) whenever \(n\) is a nonnegative integer.

Exercises \(49-51\) present incorrect proofs using mathematical induction. You will need to identify an error in reasoning in each exercise. What is wrong with this "proof" that all horses are the same color? Let \(P(n)\) be the proposition that all the horses in a set of \(n\) horses are the same color. Basis Step: Clearly, \(P(1)\) is true. Inductive Step: Assume that \(P(k)\) is true, so that all the horses in any set of \(k\) horses are the same color. Consider any \(k+1\) horses; number these as horses \(1,2,3, \ldots, k, k+1 .\) Now the first \(k\) of these horses all must have the same color, and the last \(k\) of these must also have the same color. Because the set of the first \(k\) horses and the set of the last \(k\) horses overlap, all \(k+1\) must be the same color. This shows that \(P(k+1)\) is true and finishes the proof by induction.

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