求解一个ACM基础题

求解一个ACM基础题
因为我暂时没学算法，导致做这个题目时，程序超时，以下是题目：
Description：
We know that if a phone number A is another phone number B’s prefix, B is not able to be called. For an example, A is 123 while B is 12345, after pressing 123, we call A, and not able to call B.
Given N phone numbers, your task is to find whether there exits two numbers A and B that A is B’s prefix.

Input：
The input consists of several test cases.
The first line of input in each test case contains one integer N (0<N<1001), represent the number of phone numbers.
The next line contains N integers, describing the phone numbers.
The last case is followed by a line containing one zero.

Output：
For each test case, if there exits a phone number that cannot be called, print “NO”, otherwise print “YES” instead.

Sample Input：
2
012
012345
2
12
012345
0

Sample Output：
NO
YES