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Held: Friday, 1 October 2004
Summary: Today we visit one of Java's core data structures: the array. We consider two applications of arrays in writing algorithms.
Related Pages:
Due
Assignments
Overview:
Fraction
classes allowed
you to group logical aspects of a Fraction into a whole.
type[] name = new type[size];
stuff
,
you would write
double[] stuff = new double[5];
type[] name = { val1, val2, ..., valn } ;
int[] stuff = {3, 2, 6, 5};
name[index]
stuff
with
stuff[3]
i
held the value 3, then we could get
element 3 of the stuff
with
stuff[i]
name.length
public double sum(double[] stuff) { double total = 0; // The total of the numbers in stuff int i; // A counter variable for stepping through // the array // Step through the array, adding each subsequent value for(i = 0; i < stuff.length; i = i + 1) { total = total + stuff[i]; } // Return the total value return total; } // sum
public long fib(int n) { if (n < 2) return n; else return fib(n-1) + fib(n-2); } // fib(int)
public long fibra(int n) { // Build a cache, use -1 for "I don't know." int cache = new long[n+1]; cache[0] = 0; cache[1] = 1; for (int i = 2; i <= n; i++) cache[i] = -1; // Compute the nth number using the cache. fibra_helper(n, cache); } // fibra(int) public long fibra_helper(int n, long[] cache) { // If the cache contains no value if (cache[n] == -1) // Compute it cache[n] = fibra_helper(n-1, cache) + fibra_helper(n-2, cache); // The cache must now return a value, so // return it. return cache[n]; } // fibra_helper * Since each element of the array gets filled in once, this is a much faster algorithm. * The idea of caching values is often called dynamic programming. It's one of the algorithm design strategies you'll often employ.An Iterative Implementation
Back to Project Discussion. On to Documentation and JavaDoc.
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Groupings:
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[Handouts]
[Homework]
[Labs]
[Outlines]
[Readings]
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Misc:
[SamR]
[Java 1.4.2 API]
[EIJ]
[CS152 2000F]
[CS153 2004S]
Disclaimer:
I usually create these pages on the fly
, which means that I rarely
proofread them and they may contain bad grammar and incorrect details.
It also means that I tend to update them regularly (see the history for
more details). Feel free to contact me with any suggestions for changes.
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The source to the document was last modified on Thu Aug 26 20:22:23 2004.
This document may be found at http://www.cs.grinnell.edu/~rebelsky/Courses/CS152/2004F/Outlines/outline.21.html
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