【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：

#include <iostream>
#include <vector>
#include <string>
using namespace std;

//node structure in Trie tree
struct Node
{
Node(char _chr = -1){chr = _chr; cnt = 0;}
char chr;
vector<Node*> nexts;
int cnt;//how many strings pass current node
};

int main()
{
Node* root = new Node;//root of dictornary
Node* current;
vector<Node*> v_current;
int cnt, vsize, i, j, strLen;
string str;

//create Trie tree
cin>>cnt;
while(cnt-- > 0)
{
cin>>str;
strLen = str.length();
current = root;
for(i = 0; i < strLen; i++)
{
v_current = current->nexts;
vsize = v_current.size();
//try to find str[i] in current tree
for(j = 0; j < vsize; j++)
{
if(v_current[j]->chr == str[i])
break;
}
if(j == vsize)//not found, create a new node
{
Node* tmp = new Node(str[i]);
current->nexts.push_back(tmp);
}
current = current->nexts[j];
current->cnt++;//increase count of current node
}
}

cin>>cnt;
while(cnt-- > 0)
{
cin>>str;
strLen = str.length();
current = root;
for(i = 0; i < strLen; i++)
{
v_current = current->nexts;
vsize = v_current.size();
for(j = 0; j < vsize; j++)
if(v_current[j]->chr == str[i])
break;
if(j == vsize)//not found
{
cout<<'0'<<endl;
break;
}
current = v_current[j];
}
if(i == strLen)
cout<<current->cnt<<endl;
}
return 0;
}

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