【Hihocoder】1014 : Trie树

问题：http://hihocoder.com/problemset/problem/1014

给定一个字符串字典dict，输入字符串str, 要求从dict中找出所有以str为前缀的字符串个数。

构建Trie树：

1) 一个节点有多个子节点。用vector<Node*> nexts 存储。

2) 两个字符串的相同前缀部分共用同一条路径。

3) 每个节点包含计数变量 cnt，表示有多少个字符串共用该节点

复杂度分析：

假定dict中的字符串个数 n, 字符串的长度 l

1）建树：O(n^2*l)

2) 查找：O(n*l)

源码：

 1 #include <iostream>
 2 #include <vector>
 3 #include <string>
 4 using namespace std;
 5 
 6 //node structure in Trie tree
 7 struct Node
 8 {
 9   Node(char _chr = -1){chr = _chr; cnt = 0;}
10   char chr;
11   vector<Node*> nexts;
12   int cnt;//how many strings pass current node
13 };
14 
15 int main()
16 {
17     Node* root = new Node;//root of dictornary
18     Node* current;
19     vector<Node*> v_current;
20     int cnt, vsize, i, j, strLen;
21     string str;
22     
23     //create Trie tree
24     cin>>cnt;
25     while(cnt-- > 0)
26     {
27         cin>>str;
28         strLen = str.length();
29         current = root;
30         for(i = 0; i < strLen; i++)
31         {
32             v_current = current->nexts;
33             vsize = v_current.size();
34             //try to find str[i] in current tree
35             for(j = 0; j < vsize; j++)
36             {
37                 if(v_current[j]->chr == str[i])
38                     break;
39             }
40             if(j == vsize)//not found, create a new node
41             {
42                 Node* tmp = new Node(str[i]);
43                 current->nexts.push_back(tmp);
44             }
45             current = current->nexts[j];
46             current->cnt++;//increase count of current node
47         }
48     }
49         
50     cin>>cnt;
51     while(cnt-- > 0)
52     {
53         cin>>str;
54         strLen = str.length();
55         current = root;
56         for(i = 0; i < strLen; i++)
57         {
58             v_current = current->nexts;
59             vsize = v_current.size();
60             for(j = 0; j < vsize; j++)
61                 if(v_current[j]->chr == str[i])
62                     break;
63             if(j == vsize)//not found
64             {
65                 cout<<'0'<<endl;
66                 break;
67             }
68             current = v_current[j];
69         }
70         if(i == strLen)
71             cout<<current->cnt<<endl;
72     }
73     return 0;
74 }

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