算法（Algorithms）第4版 练习 1.3.27 1.3.28

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<Integer> 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<Integer> 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<Integer> list = new LinkedList<Integer>();
        
        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: 90
90 
insertAtBeginning success: 78
78 90 
The maximum key is:90
The maximum key is:90(By Recursion)

测试数据3：

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

测试数据4（输入为空）：

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