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hw1 - CSCI 4041 Algorithms and Data Structures(Fall09...

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CSCI 4041: Algorithms and Data Structures (Fall’09) Homework 1, Due 09/24/09 Answer all of the following questions, and always explain your answer. Good Luck! 1. (50 points) Consider the following sorted search problem: Input: A sequence of n distinct sorted numbers A = h a 1 , a 2 , . . . , a n i and a number v . Output: An index i such that A [ i ] v < A [ i + 1] . If v < a 1 , then output 0. If v a n , then output n . (a) (15 points) Give an algorithm (pseudo-code) for solving the problem by scanning the entire sequence. Using a loop invariant, show that your algorithm is correct. (b) (15 points) Instead of scanning the entire sequence, since A is sorted, we can check the midpoint of the sequence against v and eliminate half of the sequence from further consideration. Binary search is an algorithm that repeats this procedure, halving the size of the remaining portion of the sequence each time. Write pseudocode, either iterative or recursive, for binary search. Argue that the worst-case running time of binary search is
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