Question

In JAVA...

Implement size(), delete(), and keys() for SequentialSearchST.

Answer 1

public class SequentialSearchST<Key, Value> {
private int n; // number of key-value pairs
private Node first; // the linked list of key-value pairs

// a helper linked list data type
private class Node {
private Key key;
private Value val;
private Node next;

public Node(Key key, Value val, Node next) {
this.key = key;
this.val = val;
this.next = next;
}
}

/**
* Initializes an empty symbol table.
*/
public SequentialSearchST() {
}

/**
* Returns the number of key-value pairs in this symbol table.
* (atrate)return the number of key-value pairs in this symbol table
*/
public int size() {
return n;
}

/**
* Is this symbol table empty?
* (atrate)return {(atrate)code true} if this symbol table is empty and {(atrate)code false} otherwise
*/
public boolean isEmpty() {
return size() == 0;
}

/**
* Does this symbol table contain the given key?
* (atrate)param key the key
* (atrate)return {(atrate)code true} if this symbol table contains {(atrate)code key} and
* {(atrate)code false} otherwise
*/
public boolean contains(Key key) {
return get(key) != null;
}

/**
* Returns the value associated with the given key.
* (atrate)param key the key
* (atrate)return the value associated with the given key if the key is in the symbol table
* and {(atrate)code null} if the key is not in the symbol table
*/
public Value get(Key key) {
for (Node x = first; x != null; x = x.next) {
if (key.equals(x.key))
return x.val;
}
return null;
}

/**
* Inserts the key-value pair into the symbol table, overwriting the old value
* with the new value if the key is already in the symbol table.
* If the value is {(atrate)code null}, this effectively deletes the key from the symbol table.
* (atrate)param key the key
* (atrate)param val the value
*/
public void put(Key key, Value val) {
if (val == null) {
delete(key);
return;
}

for (Node x = first; x != null; x = x.next) {
if (key.equals(x.key)) {
x.val = val;
return;
}
}
first = new Node(key, val, first);
n++;
}

/**
* Removes the key and associated value from the symbol table
* (if the key is in the symbol table).
* (atrate)param key the key
*/
public void delete(Key key) {
first = delete(first, key);
}

// delete key in linked list beginning at Node x
// warning: function call stack too large if table is large
private Node delete(Node x, Key key) {
if (x == null) return null;
if (key.equals(x.key)) {
n--;
return x.next;
}
x.next = delete(x.next, key);
return x;
}

/**
* Returns all keys in the symbol table as an {(atrate)code Iterable}.
* To iterate over all of the keys in the symbol table named {(atrate)code st},
* use the foreach notation: {(atrate)code for (Key key : st.keys())}.
* (atrate)return all keys in the symbol table as an {(atrate)code Iterable}
*/
public Iterable<Key> keys() {
Queue<Key> queue = new Queue<Key>();
for (Node x = first; x != null; x = x.next)
queue.enqueue(x.key);
return queue;
}

/**
* Unit tests the {(atrate)code SequentialSearchST} data type.
*
* (atrate)param args the command-line arguments
*/
public static void main(String[] args) {
SequentialSearchST<String, Integer> st = new SequentialSearchST<String, Integer>();
for (int i = 0; !StdIn.isEmpty(); i++) {
String key = StdIn.readString();
st.put(key, i);
}
for (String s : st.keys())
StdOut.println(s + " " + st.get(s));
}
}