链接:https://codeforces.ml/contest/1303/problem/C
Polycarp wants to assemble his own keyboard. Layouts with multiple rows are too complicated for him — his keyboard will consist of only one row, where all 2626 lowercase Latin letters will be arranged in some order.
Polycarp uses the same password ss on all websites where he is registered (it is bad, but he doesn't care). He wants to assemble a keyboard that will allow to type this password very easily. He doesn't like to move his fingers while typing the password, so, for each pair of adjacent characters in ss, they should be adjacent on the keyboard. For example, if the password is abacaba, then the layout cabdefghi... is perfect, since characters a and c are adjacent on the keyboard, and a and b are adjacent on the keyboard. It is guaranteed that there are no two adjacent equal characters in ss, so, for example, the password cannot be password (two characters sare adjacent).
Can you help Polycarp with choosing the perfect layout of the keyboard, if it is possible?
Input
The first line contains one integer TT (1≤T≤10001≤T≤1000) — the number of test cases.
Then TT lines follow, each containing one string ss (1≤|s|≤2001≤|s|≤200) representing the test case. ss consists of lowercase Latin letters only. There are no two adjacent equal characters in ss.
Output
For each test case, do the following:
- if it is impossible to assemble a perfect keyboard, print NO (in upper case, it matters in this problem);
- otherwise, print YES (in upper case), and then a string consisting of 2626 lowercase Latin letters — the perfect layout. Each Latin letter should appear in this string exactly once. If there are multiple answers, print any of them.
Example
input
Copy
5 ababa codedoca abcda zxzytyz abcdefghijklmnopqrstuvwxyza
output
Copy
YES bacdefghijklmnopqrstuvwxyz YES edocabfghijklmnpqrstuvwxyz NO YES xzytabcdefghijklmnopqrsuvw NO
代码:
#include<bits/stdc++.h>
using namespace std;
long long t,n;
map<char,bool> flag;
int main()
{
cin>>t;
while(t--)
{
for(char j='a';j<='z';j++)
flag[j]=0;
string s,ans="";
cin>>s;
int len=s.length(),k=1,now,flag1=1,len1=0;
ans+=s[0];
now=0;
flag[s[0]]=1;
for(int j=1;j<len;j++)
{
if(flag[s[j]])
{
if(ans[now-1]!=s[j]&&ans[now+1]!=s[j])
{
flag1=0;
break;
}
if(ans[now-1]==s[j])
{
k=-1;
now-=1;
}
else
{
k=1;
now+=1;
}
}
else
{
flag[s[j]]=1;
if(k==-1&&now!=0||k==1&&now!=len1)
{
flag1=0;
break;
}
if(k==-1)
{
len1++;
ans=s[j]+ans;
}
else
{
now++;
len1=max(len1,now);
ans+=s[j];
}
}
}
if(flag1)
{
cout<<"YES\n";
for(char j='a';j<='z';j++)
{
if(!flag[j])
ans+=j;
}
cout<<ans<<endl;
}
else
cout<<"NO\n";
}
return 0;
}

解决Codeforces上关于创建完美键盘布局的问题,使特定字符串输入时手指无需移动。通过算法确定字母排列,确保相邻字符在密码中也是键盘上的邻居。
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