#思路
将每一行的逆序存放在strs中，然后找strs中的所有line的相同前缀。
#代码1
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using namespace std;
int main()
{
int n;
scanf("%d",&n);
int enter;// the '\n' followed n
scanf("%c",&enter);
vector<string> strs;
while(n--)// push back all the lines
{
char tmpc[266];
int pos=0;
while(scanf("%c",&tmpc[pos]) && tmpc[pos] !='\n') pos++;
tmpc[pos] = '\0';
string tmp = tmpc;
reverse(tmp.begin(),tmp.end());
strs.push_back(tmp);
}
int pos = 0;
bool flag=true;
while(flag)
{
char target = strs[0][pos];
for(int i=1;i<strs.size();++i)
{
if(pos < strs[i].size())
{
if(strs[i][pos] != target)
{flag= false;break;}
}
else {flag= false;break;}//exceed the size of strs[i]
}
pos++;
}
string result = strs[0].substr(0,pos-1);
reverse(result.begin(),result.end());
if(result.size())
cout<<result<<endl;
else
cout<<"nai"<<endl;
return 0;
}