# hbs4(1) - show why(d Give a dynamic programming algorithm...

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CS 473 HBS 4 Spring 2009 CS 473: Undergraduate Algorithms, Spring 2009 HBS 4 1. Let x and y be two elements of a set S whose ranks differ by exactly r . Prove that in a treap for S , the expected length of the unique path from x to y is O ( log r ) 2. Consider the problem of making change for n cents using the least number of coins. (a) Describe a greedy algorithm to make change consisting of quarters, dimes, nickels, and pennies. Prove that your algorithm yields an optimal solution. (b) Suppose that the available coins have the values c 0 , c 1 ,..., c k for some integers c > 1 and k 1. Show that the greedy algorithm always yields an optimal solution. (c) Give a set of 4 coin values for which the greedy algorithm does not yield an optimal solution,
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Unformatted text preview: show why. (d) Give a dynamic programming algorithm that yields an optimal solution for an arbitrary set of coin values. 3. A heater is a sort of dual treap, in which the priorities of the nodes are given, but their search keys are generate independently and uniformly from the unit interval [ 0,1 ] . You can assume all priorities and keys are distinct. Describe algorithms to perform the operations INSERT and DELETEMIN in a heater. What are the expected worst-case running times of your algorithms? In particular, can you express the expected running time of INSERT in terms of the priority rank of the newly inserted item? 1...
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## This note was uploaded on 01/22/2012 for the course CS 573 taught by Professor Chekuri,c during the Fall '08 term at University of Illinois, Urbana Champaign.

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