题目链接：
http://hihocoder.com/problemset/problem/1107?sid=406355
题意：
求频率不超过5的前缀的数目。字典树的遍历
代码以下：
#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
const int maxn = 10010;
const int max_size = 30;
int id(char c){
return c-'a';
}
struct Trie{
Trie *ch[max_size];
int num;
Trie(){
num = 0;
for(int i=0;i<max_size;i++)
ch[i]=NULL;
}
}*root;
void insert_str(char *s){
Trie *p = root;
p->num++;
for(int i=0; p&&s[i] ; i++){
int u = id(s[i]);
if(p->ch[u]==NULL)
p->ch[u] = new Trie;
p=p->ch[u];
p->num++;
}
}
int find_str(char *s){
Trie *p = root;
for(int i=0;p&&s[i];i++){
int u = id(s[i]);
if(p->ch[u]==NULL) return 0;
p=p->ch[u];
}
return p->num;
}
int ans;
void vis(Trie *nod){
Trie *p=nod;
if(p->num<=5&&p->num>0) {ans++;return;}
for(int i=0;i<max_size;i++)
if(p->ch[i]) vis(p->ch[i]);
}
char s[2000010];
int main()
{
int n, m;
while(~scanf("%d", &n)){
root = new Trie;
for(int i=0;i<n;i++){
scanf("%s", s);
insert_str(s);
}
ans = 0;
vis(root);
printf("%d
",ans);
}
return 0;
}