【发布时间】：2014-07-20 21:51:11
【问题描述】：
我的代码有两个我找不到或无法理解的错误，希望有人能给我一些关于如何解决这个问题的意见。对于我的删除功能，它在第 118 行和第 125 行表示找不到符号“项目”。我以为我在我的代码中清楚地说明了项目是什么。我将在下面发布我的代码，希望有人可以提供帮助。
8 public class Dictionary implements DictionaryInterface {
9
10 // private inner Node class
11 private class Node {
12 String key;
13 String value;
14 Node left;
15 Node right;
16 Node next;
17
18 Node(String k, String v) {
19 key = k;
20 value = v;
21 left = null;
22 right = null;
23 next = null;
24 }
25 }
26
27 //Fields for the IntegerList class
28 private Node root; // reference to the head Node in list
29 private int numItems; // number of items in this IntegerList
30
31 //Dictionary()
32 //constructor for the Dictionary class
33 public Dictionary() {
34 root = null;
35 numItems = 0;
36 }
37
38 // find key
39 // returns a reference to the Node containing key k in the subtree rooted at
40 // R or Null if no such Node exists
41 private Node findKey (String key){
42 Node N = root;
43 while (N != null){
44 if(key.equals(N.key))
45 break;
46 N = N.next;
47 }
48 }
49
50 // ADT operations ---------------------------------------------
51
52 // isEmpty()
53 // pre: none
54 // post: returns true if this Dictionary is empty, false otherwise
55 public boolean isEmpty() {
56 return (numItems == 0);
57 }
58
59 // size()
60 // pre: none
61 // post: returns the number of elements in this Dictionary
62 public int size() {
63 return numItems;
64 }
65
66 // lookup(String key)
67 // get()
68 // pre: 1<= key <= size()
69 // post: returns item at position key in this Dictionary
70 public String lookup(String key){
71 Node N = root;
72 while( N != null){
73 if(key.equals(N.key))
74 break;
75 N = N.next;
76 }
77 if( N != null){
78 return N.value;
79 }else{
80 return null;
81 }
82 }
83
84
85 // insert(String key, String value)
86 // inserts new (key, value) pair into this Dictionary
87 // pre: key k does not exist in this Dictionary, i.e lookup(k) == UNDEFINED
88 // post: !isEmpty(), size() is increased by one
89 public void insert(String k, String v) throws KeyCollisionException{
90 // Node N = root;
91 if (lookup(k) != null){
92 throw new KeyCollisionException("cannot insert duplicate keys");
93 }
94 if (numItems== 0) {
95 root = new Node(k,v);
96 }else{
97 Node N = new Node(k,v);
98 N=N.next;
99 }
100 Node P = null; //N
101 Node C = P.next;
102 P.next = new Node (k, v);
103 P = P.next;
104 P.next = C;
105
106 numItems++;
107
108 }
109
110 // delete(String key)
111 // pre: key k currently exists in this Dictionary, i.e. lookup(k)!= UNDEFINED
112 // post: size() is decreased by one
113 public void delete(String k) throws KeyNotFoundException{
114 Node N = root;
115 if (lookup (k) == null){
116 throw new KeyNotFoundException("cannot delete non-existent key");
117 }
118 if (k.compareTo(N.item)==0) {
119 Node P = root;
120 root = root.next;
121 P.next = root;
122 numItems--;
123 }else{
124 while(N !=null && N.next !=null){
125 if (k.compareTo(N.next.item)==0){
126 Node P = N;
127 Node C = P.next;
128 P.next = C.next;
129 N=P;
130 }
131 N=N.next;
132 }
133 numItems--;
134 }
135 }
136
137 // makeEmpty()
138 // pre: none
139 // post: isEmpty()
140 public void makeEmpty(){
141 root = null; // root = 0;
142 numItems = 0;
143 }
【问题讨论】：
-
Node中没有属性Item。 -
Node 类中的 item 属性在哪里？
-
类
Node不包含名为item的成员 -
所以一旦我创建了 String item 是否有意义让 item = k??
-
@jpw 根据方法的描述，我认为应该是比较k和
key，而不是value。
标签： java algorithm dictionary