COP 3530, Discrete Data Structures and Algorithms, Summer 1999, Homework 4

Class Notes: Data Structures and Algorithms

Summer-C Semester 1999 - M WRF 2nd Period CSE/E119, Section 7344

Homework #4 -- Due Wed 16 June 1999 : 09.30am -- Answer Key

Answers are in blue typeface.

* Question 1. Write pseudocode and a diagram that shows how to implement the merge part of the merge-sort algorithm using two stacks (one for each subsequence), and be sure to use the correct ADT operations for stacks. Do not write Java code, or pseudocode for merge-sort.

Answer:

1. Put the two sorted subsequences to be merged, denoted by S1 and S2 on stacks of the same name. Assume that the sorting is in ascending order; hence, each stack has its minimum values at the top of the stack.

2. The merge algorithm proceeds as follows:

{ repeat until S1 or S2 is empty

{ v1 = pop(S1)

v2 = pop(S2)

output(min(v1,v2))

if (max(v1,v2) = v1) then

push v1 onto S1

else

push v2 onto S2

endif

}