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| #include <bits/stdc++.h>
#define int long long
#define N 1000005
using namespace std;
int n;
signed main(){
string str,ans;cin>>str;
n = str.size();
int num[N],cnt = 0,cha = -1;memset(num,0,sizeof(num));
for(int i = 0;i < n;i++){
num[str[i] - 'A'] += 1;
}
for(int i=0;i<26;i++){
if(num[i] & 1){
cnt++;cha = i;
}
}
ans.resize(n);
if(cnt > 1)cout<<"NO SOLUTION\n";
else if(cnt == 1 && !(n&1))cout<<"NO SOLUTION\n";
else if(cnt < 1 && n&1)cout<<"NO SOLUTION\n";
else{
if(n & 1){
ans[n/2] = 'A'+cha;
num[cha]--;
}
int l = 0,r = n-1;
for(int i=0;i<26;i++){
while(num[i]){
ans[l++] = i + 'A';
ans[r--] = i + 'A';
num[i] -= 2;
}
}
cout<<ans<<"\n";
}
}
|