算法（Algorithms）第4版 练习 1.3.42

After copy
Left on Stack r: be to not or be to
Left on Stack copy: be to not or be to
After r pop
Left on Stack r: to not or be to
Left on Stack copy: be to not or be to 

//1.3.42
        Stack<String> r = new Stack<String>(copy);
        StdOut.println("After copy");
        StdOut.print("Left on Stack r: ");
        for (String s : r) {
            StdOut.print(s + " ");
        }
        StdOut.println();
        StdOut.print("Left on Stack copy: ");
        for (String s : copy) {
            StdOut.print(s + " ");
        }
        StdOut.println();

        r.pop();
        StdOut.println("After r pop");
        StdOut.print("Left on Stack r: ");
        for (String s : r) {
            StdOut.print(s + " ");
        }
        StdOut.println();
        StdOut.print("Left on Stack copy: ");
        for (String s : copy) {
            StdOut.print(s + " ");
        }
        StdOut.println();

    //1.3.42
    public Stack(Stack<Item> stack) {

        first = null;
        n = 0;

        Stack<Item> temp = new Stack<Item>();

        for(Item item : stack) {
            temp.push(item);
        }
        for(Item item : temp) {
            this.push(item);
        }

    }