题目链接：
?sid=406355
题意：
求频率不超过5的前缀的数目。字典树的遍历
代码如下：
#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\n",ans); } return 0;}
，对于旅行，从来都记忆模糊。记不得都去了哪些地方，
