java/12-structures/FrequencyTable Source

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Description
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The class <tt>FrequencyTable</tt> represents a table that tracks
the number of repeated occurrences of items in a list of Strings. It has
the API
<pre>
public FrequencyTable() // new table
public void click(String word) // add 1 to frequency of this word
public int count(String word) // what is frequency of this word?
public void show() // print out all words and frequencies
</pre>
For example,
<pre>
FrequencyTable ft = new FrequencyTable();
ft.click("duck");
ft.click("duck");
ft.click("goose");
StdOut.println(ft.count("duck")); // should print 2
StdOut.println(ft.count("goose")); // should print 1
StdOut.println(ft.count("horse")); // should print 0
</pre>
In addition, create a <tt>main</tt> that takes no arguments, reads words
from standard input (using <tt>StdIn.readString()</tt>) until none are left,
and then prints out the frequencies of all words using <tt>show()</tt>.
<div class="noprint">
You will need to know the <a href="http://introcs.cs.princeton.edu/java/44st/"><tt>ST</tt> API</a>: look up the constructor, <tt>put</tt> and <tt>get</tt>.
</div>
<div class="printonly">
Here are the relevant components of the ST API:
<pre>public class ST<Key, Value> // Note: Key must be Comparable
------------------------------------------------------------------------
ST<Key, Value>() // create a symbol table
void put(Key key, Value v) // put key-value pair into the table
Value get(Key key) // return value paired with key
// or null if no such value
boolean contains(key Key) // is there a value paired with key?
// Allows iteration with enhanced for loops:
for (Key key : st) {...} // executes body once for each key
</pre>
</div>

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Choices
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Correct answer
Template / Reference solution

// Dependencies: ST.java (available on precepts page), StdIn, StdOut
// maintain counts of all words seen so far
// the key is the word and the value is the count
private ST<\[String, Integer]\> st = \[new ST<String, Integer>()]\;

// remark: we have not declared a constuctor! but Java lets every class
// have a no-argument constructor by default. It only runs the line of
// code above (instance variable initialization).

// add 1 to the frequency of this word
public void click(String word) {
int count = count(word);
st.put(word, count + 1);
}

// what is the frequency of this word?
public int count(String word) {
if (!st.\[contains]\(\[word]\)) return 0; // if word is not in ST
else return \[st]\.\[get]\(\[word]\); // get word's count
}

// print out all words and frequencies
public void show() {
// foreach loop. goes through all keys in alphabetical order
for (String word : st) {
// print out frequency and word, separated by a space
StdOut.println(\[count]\(\[word]\) + " " + \[word]\);
}
}

// method used by client to count all words in StdIn
public static void main(String[] args) {

// build frequency table from words on standard input
FrequencyTable freq = new FrequencyTable();
while (!StdIn.isEmpty()) {
String word = StdIn.readString();
freq.\[click]\(word);
}

// print frequency table to standard output
freq.show();
}

Template / Reference solution

Java test suite
See manual

saveAs = "ft";
testConstructor();
testOn("ft", "click", "duck");
testOn("ft", "count", "duck");
testOn("ft", "click", "duck");
testOn("ft", "click", "goose");
testOn("ft", "count", "duck");
testOn("ft", "count", "goose");
testOn("ft", "count", "horse");
stdin = "in this test the api is tested by the words in the sentence";
testMain();
maxOutputBytes = 500000;
stdinURL = "http://introcs.cs.princeton.edu/java/44st/mobydick.txt";
testMain();

C++ test suite
json list of stdin/args tests
e.g. [{"stdin":"hi", "args":["4", "5"]}, {"stdin":"noargs"}]
to just run once with no input use [{}]

C++ test suite
See manual

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Property	Value
Description html markup shown to student	The class <tt>FrequencyTable</tt> represents a table that tracks the number of repeated occurrences of items in a list of Strings. It has the API <pre> public FrequencyTable() // new table public void click(String word) // add 1 to frequency of this word public int count(String word) // what is frequency of this word? public void show() // print out all words and frequencies </pre> For example, <pre> FrequencyTable ft = new FrequencyTable(); ft.click("duck"); ft.click("duck"); ft.click("goose"); StdOut.println(ft.count("duck")); // should print 2 StdOut.println(ft.count("goose")); // should print 1 StdOut.println(ft.count("horse")); // should print 0 </pre> In addition, create a <tt>main</tt> that takes no arguments, reads words from standard input (using <tt>StdIn.readString()</tt>) until none are left, and then prints out the frequencies of all words using <tt>show()</tt>. <div class="noprint"> You will need to know the <a href="http://introcs.cs.princeton.edu/java/44st/"><tt>ST</tt> API</a>: look up the constructor, <tt>put</tt> and <tt>get</tt>. </div> <div class="printonly"> Here are the relevant components of the ST API: <pre>public class ST<Key, Value> // Note: Key must be Comparable ------------------------------------------------------------------------ ST<Key, Value>() // create a symbol table void put(Key key, Value v) // put key-value pair into the table Value get(Key key) // return value paired with key // or null if no such value boolean contains(key Key) // is there a value paired with key? // Allows iteration with enhanced for loops: for (Key key : st) {...} // executes body once for each key </pre> </div>
Epilogue html markup shown when solved	remove
Public permissions	remove
Remarks Comments, history, license, etc.	remove
Engine
Choices json list of string, bool pairs e.g. `[["good", true], ["bad", false]]`
Correct answer
Template / Reference solution	// Dependencies: ST.java (available on precepts page), StdIn, StdOut // maintain counts of all words seen so far // the key is the word and the value is the count private ST<\[String, Integer]\> st = \[new ST<String, Integer>()]\; // remark: we have not declared a constuctor! but Java lets every class // have a no-argument constructor by default. It only runs the line of // code above (instance variable initialization). // add 1 to the frequency of this word public void click(String word) { int count = count(word); st.put(word, count + 1); } // what is the frequency of this word? public int count(String word) { if (!st.\[contains]\(\[word]\)) return 0; // if word is not in ST else return \[st]\.\[get]\(\[word]\); // get word's count } // print out all words and frequencies public void show() { // foreach loop. goes through all keys in alphabetical order for (String word : st) { // print out frequency and word, separated by a space StdOut.println(\[count]\(\[word]\) + " " + \[word]\); } } // method used by client to count all words in StdIn public static void main(String[] args) { // build frequency table from words on standard input FrequencyTable freq = new FrequencyTable(); while (!StdIn.isEmpty()) { String word = StdIn.readString(); freq.\[click]\(word); } // print frequency table to standard output freq.show(); }
Template / Reference solution
Java test suite See manual	saveAs = "ft"; testConstructor(); testOn("ft", "click", "duck"); testOn("ft", "count", "duck"); testOn("ft", "click", "duck"); testOn("ft", "click", "goose"); testOn("ft", "count", "duck"); testOn("ft", "count", "goose"); testOn("ft", "count", "horse"); stdin = "in this test the api is tested by the words in the sentence"; testMain(); maxOutputBytes = 500000; stdinURL = "http://introcs.cs.princeton.edu/java/44st/mobydick.txt"; testMain();
C++ test suite json list of stdin/args tests e.g. `[{"stdin":"hi", "args":["4", "5"]}, {"stdin":"noargs"}]` to just run once with no input use `[{}]`
C++ test suite See manual
Forbidden substrings json list of strings e.g. `["for","while"]`	remove
Solution visibility	remove
Java imports json list of importables e.g. `["java.util.*"]`	remove
Override Java classname else defaults to websheet name	remove
Dependent on other websheets? json list of websheet names in this folder e.g. `["DataStructure"]`	remove
Is example? i.e., just a demo	remove
Add compiler flag(s) json list of flags e.g. `["-Wno-unused-variable"]`	remove
Remove default compiler flag(s) json list of flags see default_cppflags e.g. `["-Wno-write-strings"]`	remove

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