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CMSC 150INTRODUCTION
TOCOMPUTING
CS 150: Mon 9 Jan 2012
About Me
Dr. Lewis Barnett Office: 212A Jepson Hall Office Hours: Most anytime, but
especiallyMT 2:30 - 3:30 pm; WR 10:30 - 11:30 am;
lbarnett@richmond.edu http://www.mathcs.richmond.edu/~lbarnett/
First: Meet Doug
He Decides Network Connections
Connections Doug Can Choose
Hours to Install Each Connection
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What Doug Wants…
A set of connections so that: a connection to each place (no place left
out) no loops sum of all installation times is minimum
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three loops here
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one loop here
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no loops here
Start With A Smaller Example
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Which connections should you include?5
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Start With A Smaller Example
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Which connections should you include? Likely the shorter ones…
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Start With A Smaller Example
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Which connections should you include? Likely the shorter ones Less likely the longer ones…
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Step by Step…
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Step by Step…
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Step by Step…
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Step by Step…
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Step by Step…
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Step by Step…
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loop!
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Step by Step…
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Step by Step…
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− each place connected− no loops− sum of times is minimum5
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Minimal vs. Not
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− each place connected− no loops− sum of times is minimum
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54 − each place connected
− no loops− sum of times is NOT minimum
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You Try It…
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Was This Your Result ?
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− each place is connected− no loops− sum of times is minimum: 28 hours
Doug is a Happy Fellow!
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Your Next Task
Break into pairs…
Write down the procedure you used: think in general terms
how do you start? how do you proceed from there? when do you finish?
Your Algorithm
You have just written down your first algorithm Kruskal’s algorithm for finding Minimum
Spanning Tree
1. Include path with min time (ties broken arbitrarily)
2. Include next shortest path if it does not introduce a loop
3. Repeat step 2 until each place has a path connected to it
Algorithms
Algorithm: Set of instructions for solving a problem known starting condition well-defined sequence of steps terminates
Computation: applying an algorithm to an input to obtain an output (solution)
Key: different algorithms can solve same problem Choose the “best” algorithm
Applications of MST
Network Design computer, electrical, cable, road, … e.g., want set of lines that connects all
offices with minimum total cost
Real-time face verification Particle interactions in fluid flows Ethernet bridging to avoid cycles in
network
About This Course
An introduction to the science of computing
You will learn: how to think algorithmically how to write your solutions in a program
(in Java) how to debug and test your solutions
Remember…
Computer science is not (just) programming
Computer scientists do much more than program
They develop algorithms to solve
problems using the computer (and programs) incorporating a variety of disciplines myriad applications and real-world
benefits…
But We Have To Start Simple…
JavaProgra
m(Source)
Compiler
JavaProgra
m(Byte Code)
You write the source codein an IDE, e.g., BlueJ
But We Have To Start Simple…
JavaProgra
m(Source)
Compiler
JavaProgra
m(Byte Code)
The compiler is a program thatconverts source to binary; Included in BlueJ
But We Have To Start Simple…
JavaProgra
m(Source)
Compiler
JavaProgra
m(Byte Code)
Byte code version can be executed on computer
Let’s Write Our First Program !