CodeForces 278BNew Problem

E - New Problem

Time Limit:2000MS     Memory Limit:262144KB     64bit IO Format:%I64d & %I64u

Submit Status Practice CodeForces 278B

Description

Coming up with a new problem isn't as easy as many people think. Sometimes it is hard enough to name it. We'll consider a title originalif it doesn't occur as a substring in any titles of recent Codeforces problems.

You've got the titles of n last problems — the strings, consisting of lowercase English letters. Your task is to find the shortest original title for the new problem. If there are multiple such titles, choose the lexicographically minimum one. Note, that title of the problem can't be an empty string.

A substrings[l... r](1 ≤ l ≤ r ≤ |s|) of string s = s₁s₂... s_|s| (where |s| is the length of string s) is string s_ls_l + 1... s_r.

String x = x₁x₂... x_p is lexicographically smaller than string y = y₁y₂... y_q, if either p < q and x₁ = y₁, x₂ = y₂, ... , x_p = y_p, or there exists such number r(r < p, r < q), that x₁ = y₁, x₂ = y₂, ... , x_r = y_r and x_r + 1 < y_r + 1. The string characters are compared by their ASCII codes.

Input

The first line contains integer n (1 ≤ n ≤ 30) — the number of titles you've got to consider. Then follow n problem titles, one per line. Each title only consists of lowercase English letters (specifically, it doesn't contain any spaces) and has the length from 1 to 20, inclusive.

Output

Print a string, consisting of lowercase English letters — the lexicographically minimum shortest original title.

Sample Input

Input

5threehorsesgoodsubstringssecretprimematrixbeautifulyear

Output

j

Input

4aabdefghijklmnopqrstuvwxyzc

Output

ab

Hint

In the first sample the first 9 letters of the English alphabet (a, b, c, d, e, f, g, h, i) occur in the problem titles, so the answer is letter j.

In the second sample the titles contain 26 English letters, so the shortest original title cannot have length 1. Title aa occurs as a substring in the first title.

题意：给你一个数n，然后n行，表示文章标题，现在让你求的是最短的起初的文章标题，这个标题要求n个文章标题中都不包含（也就是不是子串）。

思路：可以看到n很小，长度也很小，直接暴力。从长度为1的串依次增加字典序，依次枚举，只要n个串中不包含这个串就是答案。

#include <iostream>#include <bits/stdc++.h>using namespace std;char s[30][25];char a[30];int n;int flag=0;void dfs(int l,int goal){    int i,j;    if(l==goal)    {        a[l]=0;        for(j=0; j<n; ++j)        {            if(strstr(s[j],a))break;//如果包含说明不符合条件        }        if(j==n)//如果符合条件        {            puts(a);            flag=1;        }        return;    }    for(i=0; i<=25; ++i)    {        a[l]=i+'a';        dfs(l+1,goal);        if(flag)return;    }}int main(){    int i;    scanf("%d",&n);    for(i=0; i<n; ++i)    {        scanf("%s",s[i]);    }    for(i=1;;++i)    {        dfs(0,i);        if(flag)break;    }    return 0;}