【LeetCode】前缀树 trie（共14题）

【208】Implement Trie (Prefix Tree) （2018年11月27日）

实现基本的 trie 树，包括 insert， search， startWith 操作等 api。

题解：《程序员代码面试指南》chp5， 最后一题。 里面讲了怎么实现。这个就看代码吧。没啥好说的了。

 1 class Trie {
 2 public:
 3     /** Initialize your data structure here. */
 4     Trie() {
 5         root = new TrieNode();
 6     }
 7     
 8     /** Inserts a word into the trie. */
 9     void insert(string word) {
10         if (word.empty()) {return;}
11         const int n = word.size();
12         TrieNode* node = root;
13         int index = 0;
14         for (int i = 0; i < n; ++i) {
15             index = word[i] - 'a';
16             if (node->mp.find(index) == node->mp.end()) {
17                 node->mp[index] = new TrieNode();
18             }
19             node = node->mp[index];
20             node->path++;
21         }
22         node->end++;
23     }
24     
25     /** Returns if the word is in the trie. */
26     bool search(string word) {
27         if (word.empty()) {return false;}
28         TrieNode* node = root;
29         const int n = word.size();
30         int index = 0;
31         for (int i = 0; i < n; ++i) {
32             index = word[i] - 'a';
33             if (node->mp.find(index) == node->mp.end()) {
34                 return false;
35             }
36             node = node->mp[index];
37             if (node->path == 0) {
38                 return false;
39             }
40         }
41         return node->end >= 1;
42     }
43     
44     /** Returns if there is any word in the trie that starts with the given prefix. */
45     bool startsWith(string prefix) {
46         if (prefix.empty()) {return false;}
47         const int n = prefix.size();
48         TrieNode* node = root;
49         int index = 0;
50         for (int i = 0; i < n; ++i) {
51             index = prefix[i] - 'a';
52             if (node->mp.find(index) == node->mp.end()) {
53                 return false;
54             }
55             node = node->mp[index];
56             if (node->path == 0) {
57                 return false;
58             }
59         }
60         return node->path >= 1;
61     }
62     
63     //define trie node
64     struct TrieNode{
65         int path;  //代表多少个单词共用这个结点
66         int end;  //代表多少个单词以这个结点结尾
67         map<int, TrieNode*> mp;
68         TrieNode() {
69             path = 0, end = 0;
70         }
71     };
72     TrieNode* root;
73 };
74 
75 /**
76  * Your Trie object will be instantiated and called as such:
77  * Trie obj = new Trie();
78  * obj.insert(word);
79  * bool param_2 = obj.search(word);
80  * bool param_3 = obj.startsWith(prefix);
81  */

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