Created
January 30, 2023 23:09
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/****************************************************************************** | |
* Compilation: javac LinkedStackOfStrings.java | |
* Execution: java LinkedStackOfStrings | |
* Data files: https://introcs.cs.princeton.edu/java/43stack/tobe.txt | |
* | |
* A stack of strings, implemented using a linked list. | |
* | |
* % more tobe.txt | |
* to be or not to - be - - that - - - is | |
* | |
* % java LinkedStackOfStrings < tobe.txt | |
* to be not that or be | |
* | |
******************************************************************************/ | |
import java.util.NoSuchElementException; | |
public class LinkedStackOfStrings { | |
private int n; // size of the stack | |
private Node first; // top of stack | |
// helper Node class | |
private class Node { | |
private String item; | |
private Node next; | |
} | |
// is the stack empty? | |
public boolean isEmpty() { | |
return first == null; | |
} | |
// number of elements on the stack | |
public int size() { | |
return n; | |
} | |
// add an element to the stack | |
public void push(String item) { | |
Node oldfirst = first; | |
first = new Node(); | |
first.item = item; | |
first.next = oldfirst; | |
n++; | |
} | |
// delete and return the most recently added element | |
public String pop() { | |
if (isEmpty()) throw new NoSuchElementException("stack underflow"); | |
String item = first.item; // save item to return | |
first = first.next; // delete first node | |
n--; | |
return item; // return the saved item | |
} | |
// test client | |
public static void main(String[] args) { | |
LinkedStackOfStrings stack = new LinkedStackOfStrings(); | |
while (!StdIn.isEmpty()) { | |
String item = StdIn.readString(); | |
if (!item.equals("-")) stack.push(item); | |
else if (stack.isEmpty()) StdOut.println("BAD INPUT"); | |
else StdOut.print(stack.pop()); | |
} | |
} | |
} |
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