链表实现堆栈

男娘i 2021-07-24 11:44 301阅读 0赞

**一 代码**

package common;
    
    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;
        }
    
        public Stack() {
            first = null;
            n = 0;
        }
    
        public boolean isEmpty() {
            return first == null;
        }
    
        public int size() {
            return n;
        }
    
        public void push(Item item) {
            Node<Item> oldfirst = first;
            first = new Node<Item>();
            first.item = item;
            first.next = oldfirst;
            n++;
        }
    
        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
        }
    
        public Item peek() {
            if (isEmpty()) throw new NoSuchElementException("Stack underflow");
            return first.item;
        }
    
        public String toString() {
            StringBuilder s = new StringBuilder();
            for (Item item : this) {
                s.append(item);
                s.append(' ');
            }
            return s.toString();
        }
    
        public Iterator<Item> iterator() {
            return new ListIterator(first);
        }
    
        // an iterator, doesn't implement remove() since it's optional
        private class ListIterator 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;
            }
        }
    
        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)");
        }
    }

**二 测试**

F:\Algorithm\target\classes>more tobe.txt
    to be or not to - be - - that - - - is
    F:\Algorithm\target\classes>java common.Stack < tobe.txt
    to be not that or be (2 left on stack)