代码实现：

//1.3.27    /**     * return the value of the maximum key in the list     *      * @param list the linked list of Integer     *      * @return return the maximum key in the list     */    public static int max(LinkedList
     
       list) {                if(list.first == null)            return 0;                int max = 0;        for(int val : list) {            if(val > max)                max = val;        }                return max;    }        //1.3.28    /**     * return the value of the maximum key in the list by recursion     *      * @param list the linked list of Integer     *      * @return return the maximum key in the list     */    public static int maxByRecursion(LinkedList
      
        list) {                if(list.first == null)            return 0;                int first = list.first.item;//first item        list.first = list.first.next;//remove first item in the list        int max = maxByRecursion(list);//calculate the maximum value of the new list                if(first > max)            return first;        else            return max;    }
      
     

测试用例：

package com.qiusongde.linkedlist;import edu.princeton.cs.algs4.StdIn;import edu.princeton.cs.algs4.StdOut;public class Exercise1327 {    public static void main(String[] args) {                LinkedList
     
       list = new LinkedList
      
       ();                while(!StdIn.isEmpty()) {            int val = StdIn.readInt();            list.insertAtBeginning(val);            StdOut.println("insertAtBeginning success: " + val);            StdOut.println(list);        }                int max = LinkedList.max(list);        StdOut.println("The maximum key is:" + max);                max = LinkedList.maxByRecursion(list);        StdOut.println("The maximum key is:" + max + "(By Recursion)");    }}
      
     

 

测试数据1：

insertAtBeginning success: 10

10

insertAtBeginning success: 25

25 10

insertAtBeginning success: 30

30 25 10

insertAtBeginning success: 100

100 30 25 10

insertAtBeginning success: 51

51 100 30 25 10

insertAtBeginning success: 26

26 51 100 30 25 10

insertAtBeginning success: 69

69 26 51 100 30 25 10

insertAtBeginning success: 6

6 69 26 51 100 30 25 10

insertAtBeginning success: 32

32 6 69 26 51 100 30 25 10

insertAtBeginning success: 78

78 32 6 69 26 51 100 30 25 10

insertAtBeginning success: 90

90 78 32 6 69 26 51 100 30 25 10

The maximum key is:100

The maximum key is:100(By Recursion)

 

测试数据2：

insertAtBeginning success: 9090 insertAtBeginning success: 7878 90 The maximum key is:90The maximum key is:90(By Recursion)

 

测试数据3：

insertAtBeginning success: 9090 The maximum key is:90The maximum key is:90(By Recursion)

 

测试数据4（输入为空）：

The maximum key is:0The maximum key is:0(By Recursion)