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#include <bits/stdc++.h> | |
#define REP(i,n) for(int i=0;i<(int)(n);i++) | |
#define ALL(x) (x).begin(),(x).end() | |
using namespace std; | |
typedef long long ll; | |
typedef long double ld; | |
const ld eps = 1e-9, pi = acos(-1.0); | |
vector<string> cond; | |
ll dfs(ll term, int n) { | |
if (n == (int)cond.size()) return term; | |
for (char c: cond[n]) { | |
int t = (c | 32) - 'a'; | |
ll f = (int)(c > 'Z') + 1; | |
if (((term >> t * 2) & 3) == 3 - f) continue; | |
if (((term >> t * 2) & 3) == f) return dfs(term, n + 1); | |
ll res = dfs(term | (f << t * 2), n + 1); | |
if (res > 0) return res; | |
term = term | ((3 - f) << t * 2); | |
} | |
return 0; | |
} | |
int main() { | |
int N; | |
while (cin >> N, N) { | |
cond.clear(); | |
vector<string> str(3); | |
REP(i,3) cin >> str[i]; | |
REP(i,N) REP(j,8) { | |
string s; | |
REP(k,3) s += str[k][i*3+1 + ((j>>k)&1)]; | |
sort(ALL(s)); | |
auto it = unique(ALL(s)); | |
s.resize(it - begin(s)); | |
cond.push_back(s); | |
} | |
sort(ALL(cond)); | |
auto it = unique(ALL(cond)); | |
cond.resize(it - begin(cond)); | |
ll term = dfs(0, 0); | |
if (term != 0) { | |
vector<string> res; | |
REP(i,26) if (((term >> i * 2) & 3) == 2) res.push_back(string(1, 'A' + i)); | |
cout << res.size(); | |
for (string s: res) cout << " " << s; | |
cout << endl; | |
} | |
else cout << -1 << endl; | |
} | |
return 0; | |
} |
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