algorithm 4th笔记(1.3)
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这里先罗列代码，其中Bag，Stack，Queue
- 三种数据结构各有各的特点，Bag是无序的，用来存放数据，然后找出满足条件的数据。Stack是先进后出，Queue是先进先出。
- 三种数据结构的实现分别有数组实现和链表实现。
- 以后补全代码。
Bag
/****************************************************************************** * Compilation: javac Bag.java * Execution: java Bag < input.txt * Dependencies: StdIn.java StdOut.java * * A generic bag or multiset, implemented using a singly-linked list. * * % more tobe.txt * to be or not to - be - - that - - - is * * % java Bag < tobe.txt * size of bag = 14 * is * - * - * - * that * - * - * be * - * to * not * or * be * to * ******************************************************************************/package edu.princeton.cs.algs4;import java.util.Iterator;import java.util.NoSuchElementException;public class Bag<Item> implements Iterable<Item> { private Node<Item> first; // beginning of bag private int n; // number of elements in bag // helper linked list class private static class Node<Item> { private Item item; private Node<Item> next; } /** * Initializes an empty bag. */ public Bag() { first = null; n = 0; } /** * Returns true if this bag is empty. * * @return {@code true} if this bag is empty; * {@code false} otherwise */ public boolean isEmpty() { return first == null; } /** * Returns the number of items in this bag. * * @return the number of items in this bag */ public int size() { return n; } /** * Adds the item to this bag. * * @param item the item to add to this bag */ public void add(Item item) { Node<Item> oldfirst = first; first = new Node<Item>(); first.item = item; first.next = oldfirst; n++; } /** * Returns an iterator that iterates over the items in this bag in arbitrary order. * * @return an iterator that iterates over the items in this bag in arbitrary order */ public Iterator<Item> iterator() { return new ListIterator<Item>(first); } // an iterator, doesn't implement remove() since it's optional private class ListIterator<Item> implements Iterator<Item> { private Node<Item> current; public ListIterator(Node<Item> first) { current = first; } public boolean hasNext() { return current != null; } public void remove() { throw new UnsupportedOperationException(); } public Item next() { if (!hasNext()) throw new NoSuchElementException(); Item item = current.item; current = current.next; return item; } } /** * Unit tests the {@code Bag} data type. * * @param args the command-line arguments */ public static void main(String[] args) { Bag<String> bag = new Bag<String>(); while (!StdIn.isEmpty()) { String item = StdIn.readString(); bag.add(item); } StdOut.println("size of bag = " + bag.size()); for (String s : bag) { StdOut.println(s); } }}Stack
/****************************************************************************** * Compilation: javac Stack.java * Execution: java Stack < input.txt * Dependencies: StdIn.java StdOut.java * Data files: http://algs4.cs.princeton.edu/13stacks/tobe.txt * * A generic stack, implemented using a singly-linked list. * Each stack element is of type Item. * * This version uses a static nested class Node (to save 8 bytes per * Node), whereas the version in the textbook uses a non-static nested * class (for simplicity). * * % more tobe.txt * to be or not to - be - - that - - - is * * % java Stack < tobe.txt * to be not that or be (2 left on stack) * ******************************************************************************/package edu.princeton.cs.algs4;import java.util.Iterator;import java.util.NoSuchElementException;public class Stack<Item> implements Iterable<Item> { private Node<Item> first; // top of stack private int n; // size of the stack // helper linked list class private static class Node<Item> { private Item item; private Node<Item> next; } /** * Initializes an empty stack. */ public Stack() { first = null; n = 0; } /** * Returns true if this stack is empty. * * @return true if this stack is empty; false otherwise */ public boolean isEmpty() { return first == null; } /** * Returns the number of items in this stack. * * @return the number of items in this stack */ public int size() { return n; } /** * Adds the item to this stack. * * @param item the item to add */ public void push(Item item) { Node<Item> oldfirst = first; first = new Node<Item>(); first.item = item; first.next = oldfirst; n++; } /** * Removes and returns the item most recently added to this stack. * * @return the item most recently added * @throws NoSuchElementException if this stack is empty */ public Item pop() { if (isEmpty()) throw new NoSuchElementException("Stack underflow"); Item item = first.item; // save item to return first = first.next; // delete first node n--; return item; // return the saved item } /** * Returns (but does not remove) the item most recently added to this stack. * * @return the item most recently added to this stack * @throws NoSuchElementException if this stack is empty */ public Item peek() { if (isEmpty()) throw new NoSuchElementException("Stack underflow"); return first.item; } /** * Returns a string representation of this stack. * * @return the sequence of items in this stack in LIFO order, separated by spaces */ public String toString() { StringBuilder s = new StringBuilder(); for (Item item : this) { s.append(item); s.append(' '); } return s.toString(); } /** * Returns an iterator to this stack that iterates through the items in LIFO order. * * @return an iterator to this stack that iterates through the items in LIFO order */ public Iterator<Item> iterator() { return new ListIterator<Item>(first); } // an iterator, doesn't implement remove() since it's optional private class ListIterator<Item> implements Iterator<Item> { private Node<Item> current; public ListIterator(Node<Item> first) { current = first; } public boolean hasNext() { return current != null; } public void remove() { throw new UnsupportedOperationException(); } public Item next() { if (!hasNext()) throw new NoSuchElementException(); Item item = current.item; current = current.next; return item; } } /** * Unit tests the {@code Stack} data type. * * @param args the command-line arguments */ public static void main(String[] args) { Stack<String> stack = new Stack<String>(); while (!StdIn.isEmpty()) { String item = StdIn.readString(); if (!item.equals("-")) stack.push(item); else if (!stack.isEmpty()) StdOut.print(stack.pop() + " "); } StdOut.println("(" + stack.size() + " left on stack)"); }}Queue
/****************************************************************************** * Compilation: javac Queue.java * Execution: java Queue < input.txt * Dependencies: StdIn.java StdOut.java * Data files: http://algs4.cs.princeton.edu/13stacks/tobe.txt * * A generic queue, implemented using a linked list. * * % java Queue < tobe.txt * to be or not to be (2 left on queue) * ******************************************************************************/package edu.princeton.cs.algs4;import java.util.Iterator;import java.util.NoSuchElementException;public class Queue<Item> implements Iterable<Item> { private Node<Item> first; // beginning of queue private Node<Item> last; // end of queue private int n; // number of elements on queue // helper linked list class private static class Node<Item> { private Item item; private Node<Item> next; } /** * Initializes an empty queue. */ public Queue() { first = null; last = null; n = 0; } /** * Returns true if this queue is empty. * * @return {@code true} if this queue is empty; {@code false} otherwise */ public boolean isEmpty() { return first == null; } /** * Returns the number of items in this queue. * * @return the number of items in this queue */ public int size() { return n; } /** * Returns the item least recently added to this queue. * * @return the item least recently added to this queue * @throws NoSuchElementException if this queue is empty */ public Item peek() { if (isEmpty()) throw new NoSuchElementException("Queue underflow"); return first.item; } /** * Adds the item to this queue. * * @param item the item to add */ public void enqueue(Item item) { Node<Item> oldlast = last; last = new Node<Item>(); last.item = item; last.next = null; if (isEmpty()) first = last; else oldlast.next = last; n++; } /** * Removes and returns the item on this queue that was least recently added. * * @return the item on this queue that was least recently added * @throws NoSuchElementException if this queue is empty */ public Item dequeue() { if (isEmpty()) throw new NoSuchElementException("Queue underflow"); Item item = first.item; first = first.next; n--; if (isEmpty()) last = null; // to avoid loitering return item; } /** * Returns a string representation of this queue. * * @return the sequence of items in FIFO order, separated by spaces */ public String toString() { StringBuilder s = new StringBuilder(); for (Item item : this) { s.append(item); s.append(' '); } return s.toString(); } /** * Returns an iterator that iterates over the items in this queue in FIFO order. * * @return an iterator that iterates over the items in this queue in FIFO order */ public Iterator<Item> iterator() { return new ListIterator<Item>(first); } // an iterator, doesn't implement remove() since it's optional private class ListIterator<Item> implements Iterator<Item> { private Node<Item> current; public ListIterator(Node<Item> first) { current = first; } public boolean hasNext() { return current != null; } public void remove() { throw new UnsupportedOperationException(); } public Item next() { if (!hasNext()) throw new NoSuchElementException(); Item item = current.item; current = current.next; return item; } } /** * Unit tests the {@code Queue} data type. * * @param args the command-line arguments */ public static void main(String[] args) { Queue<String> queue = new Queue<String>(); while (!StdIn.isEmpty()) { String item = StdIn.readString(); if (!item.equals("-")) queue.enqueue(item); else if (!queue.isEmpty()) StdOut.print(queue.dequeue() + " "); } StdOut.println("(" + queue.size() + " left on queue)"); }}阅读全文
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