下压栈抽象数据类型

痛定思痛。 2021-07-24 11:39 392阅读 0赞

**一 代码**

package common;
    
    import java.util.Iterator;
    import java.util.NoSuchElementException;
    
    public class ResizingArrayStack<Item> implements Iterable<Item> {
        private Item[] a;
        private int n;
    
        public ResizingArrayStack() {
            a = (Item[]) new Object[2];
            n = 0;
        }
    
        public boolean isEmpty() {
            return n == 0;
        }
    
        public int size() {
            return n;
        }
    
        private void resize(int capacity) {
            assert capacity >= n;
    
            Item[] temp = (Item[]) new Object[capacity];
            for (int i = 0; i < n; i++) {
                temp[i] = a[i];
            }
            a = temp;
        }
    
        public void push(Item item) {
            if (n == a.length) resize(2*a.length);    // double size of array if necessary
            a[n++] = item;                            // add item
        }
    
        public Item pop() {
            if (isEmpty()) throw new NoSuchElementException("Stack underflow");
            Item item = a[n-1];
            a[n-1] = null;                              // to avoid loitering
            n--;
            // shrink size of array if necessary
            if (n > 0 && n == a.length/4) resize(a.length/2);
            return item;
        }
    
        public Item peek() {
            if (isEmpty()) throw new NoSuchElementException("Stack underflow");
            return a[n-1];
        }
    
        public Iterator<Item> iterator() {
            return new ReverseArrayIterator();
        }
    
        private class ReverseArrayIterator implements Iterator<Item> {
            private int i;
            public ReverseArrayIterator() {
                i = n-1;
            }
    
            public boolean hasNext() {
                return i >= 0;
            }
    
            public void remove() {
                throw new UnsupportedOperationException();
            }
    
            public Item next() {
                if (!hasNext()) throw new NoSuchElementException();
                return a[i--];
            }
        }
        public static void main(String[] args) {
            ResizingArrayStack<String> stack = new ResizingArrayStack<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.ResizingArrayStack < tobe.txt
    to be not that or be (2 left on stack)