hdu 1671 Phone List（字典树）

http://acm.hdu.edu.cn/showproblem.php?pid=1671

Problem Description

Given a list of phone numbers, determine if it is consistent in the sense that no number is the prefix of another. Let’s say the phone catalogue listed these numbers:
1. Emergency 911
2. Alice 97 625 999
3. Bob 91 12 54 26
In this case, it’s not possible to call Bob, because the central would direct your call to the emergency line as soon as you had dialled the first three digits of Bob’s phone number. So this list would not be consistent.

 

Input

The first line of input gives a single integer, 1 <= t <= 40, the number of test cases. Each test case starts with n, the number of phone numbers, on a separate line, 1 <= n <= 10000. Then follows n lines with one unique phone number on each line. A phone number is a sequence of at most ten digits.

 

Output

For each test case, output “YES” if the list is consistent, or “NO” otherwise.

 

Sample Input

2 3 911 97625999 91125426 5 113 12340 123440 12345 98346

 

Sample Output

NO YES

 

字典树问题，主要是注意标记，标记每个号码的最后结尾就可以了。

代码：

#include<iostream>
using namespace std;
typedef struct node
{
    node * next[10];
    int num;
    node()
    {
        num=0;
        memset(next,NULL,sizeof(next));
    }
}Nod;
void insert_tree(Nod * head,char *str)
{
    Nod *h=head;
    int len=strlen(str);
    int i;
    for(i=0;i<len;i++)
    {
        int id=str[i]-'0';
        if(h->next[id]==NULL)
            h->next[id]=new node;
        h=h->next[id];
    }
    h->num=1;   //这个标记结尾
}
int find_tree(Nod *head,char *str)
{
    int i;
    Nod *h=head;
    int len=strlen(str);
    for(i=0;i<len;i++)
    {
        int id=str[i]-'0';
        if(h->next[id]==NULL)
            return h->num;     //这句重要
        h=h->next[id];
    }
    return 1;  //这句也重要
}
void freedom(Nod *h)
{
    int i;
    for(i=0;i<10;i++)
    {
        if(h->next[i]!=NULL)
            freedom(h->next[i]);
    }
    delete h;
}
int main()
{
    char str[20];
    int t;
    scanf("%d",&t);
    while(t--)
    {
        int i,n;
        scanf("%d",&n);
        getchar();    
        Nod *head;
        head=new node;
        int flag=0;
        for(i=0;i<n;i++)
        {
            gets(str);
            if(flag||find_tree(head,str))
                flag=1;
            else
                insert_tree(head,str);    
        }
        if(!flag)
            puts("YES");
        else
            puts("NO");
        freedom(head);
    }
    return 0;
}