Given an unlimited supply of coins of denominations, we wish to make change for a value ; that is, we wish to find a set of coins whose total value is . This might not be possible: for instance, if the denominations are and 10 then we can make change for 15 but not for 12. Give an dynamic-programming algorithm for the following problem.Input:,; .Question: Is it possible to make change for using coins of denominations ?

Short Answer

Expert verified

The algorithm is as follows:

Create an array of size

D0=Truefori=1 to V   Di=Falseforv=1 to V   forj=1 to V

      ifxjv         Dv=DvORDvxi      else         Dv=Falsereturn DV

Step by step solution

01

Define dynamic programming 

Dynamic programming is a paradigm used for writing algorithm which helps to solve some particular type of problems more efficiently by saving the solution of subproblems and using them to get the final solution. Rather than performing the same calculation again and again, the optimal solution to subproblems are calculated and stored.

02

Determine the subproblem

ConsiderDu as sub-problem such that u=1,.,v.

Thus, according to question,Du is true if it is possible to make change for v using coins denomination.x1,x2,xn

Du=TRUE;ifitispossibletomakechangeforvFALSE;otherwise

Now, takingDu as sub-problem, if it is possible to make change forv using denomination,x1,x2,xnthen it is also possible to make change for by using same denomination with the coin.

The desired recursion is:

Here, ‘’ is the value for which we finding denomination.

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Most popular questions from this chapter

Suppose two teams, A and B, are playing a match to see who is the first to win games (for some particular n). We can suppose that A and B are equally competent, so each has a 50% chance of winning any particular game. Suppose they have already played i+j games, of which A has won i and B has won j. Give an efficient algorithm to compute the probability that A will go on to win the match. For example, if i=n-1 and j=n-3 then the probability that A will win the match is 78, since it must win any of the next three games.

Consider the following variation on the change-making problem (Exercise 6.17): you are given denominations x1,x2,...,xn, and you want to make change for a value v, but you are allowed to use each denomination at most once. For instance, if the denominations are 1,5,10,20,then you can make change for 16=1+15and for 31=1+10+20but not for 40(because you can’t use 20 twice).

Input: Positive integers; x1,x2,...,xnanother integer v.

Output: Can you make change for v, using each denominationxi at most once?Show how to solve this problem in time O(nV).

Here is yet another variation on the change-making problem (Exercise 6.17). Given an unlimited supply of coins of denominations x1,x2,x3.........xnwe wish to make change for a value v using at most k coins; that is, we wish to find a set ofkcoins whose total value is v. This might not be possible: for instance, if the denominations are 5 and 10 and k=6, then we can make change for 55 but not for 65. Give an efficient dynamic-programming algorithm for the following problem. Input: ; x1,x2,x3.........xn;k;v.Question: Is it possible to make change for v using at most k coins, of denominations x1,x2,x3.........xn?

Cutting cloth. You are given a rectangular piece of cloth with dimensions X×Y, whereX and Yare positive integers, and a list of products that can be made using the cloth. For each producti[1,n] you know that a rectangle of cloth of dimensionsai×bi is needed and that the final selling price of the product is ci. Assume the,ai biandci are all positive integers. You have a machine that can cut any rectangular piece of cloth into two pieces either horizontally or vertically. Design an algorithm that determines the best return on theX×Y piece of cloth, that is, a strategy for cutting the cloth so that the products made from the resulting pieces give the maximum sum of selling prices. You are free to make as many copies of a given product as you wish, or none if desired.

The garage sale problem (courtesy of Professor Lofti Zadeh). On a given Sunday morning, there are n garage sales going on, g1,g2,g3............gn. For each garage sale gj, you have an estimate of its value to you, vj. For any two garage sales you have an estimate of the transportation cost dijof getting from gito gj. You are also given the costs d0jand dj0of going between your home and each garage sale. You want to find a tour of a subset of the given garage sales, starting and ending at home, that maximizes your total benefit minus your total transportation costs. Give an algorithm that solves this problem in time O(n22n).

(Hint: This is closely related to the traveling salesman problem.)

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