結果
| 問題 | No.470 Inverse S+T Problem |
| ユーザー |
 はむこ
|
| 提出日時 | 2018-02-21 11:30:57 |
| 言語 | C++11 (gcc 11.4.0) |
| 結果 |
WA
|
| 実行時間 | - |
| コード長 | 22,263 bytes |
| コンパイル時間 | 2,124 ms |
| コンパイル使用メモリ | 223,708 KB |
| 実行使用メモリ | 6,948 KB |
| 最終ジャッジ日時 | 2024-06-01 22:54:34 |
| 合計ジャッジ時間 | 3,231 ms |
|
ジャッジサーバーID （参考情報） |
judge4 / judge2 |
（要ログイン）
テストケース
テストケース表示| 入力 | 結果 | 実行時間 実行使用メモリ |
|---|---|---|
| testcase_00 | WA | - |
| testcase_01 | AC | 1 ms
6,944 KB |
| testcase_02 | AC | 1 ms
6,940 KB |
| testcase_03 | WA | - |
| testcase_04 | AC | 1 ms
6,940 KB |
| testcase_05 | AC | 1 ms
6,944 KB |
| testcase_06 | AC | 2 ms
6,944 KB |
| testcase_07 | AC | 1 ms
6,940 KB |
| testcase_08 | AC | 1 ms
6,944 KB |
| testcase_09 | WA | - |
| testcase_10 | WA | - |
| testcase_11 | WA | - |
| testcase_12 | WA | - |
| testcase_13 | WA | - |
| testcase_14 | WA | - |
| testcase_15 | AC | 1 ms
6,940 KB |
| testcase_16 | WA | - |
| testcase_17 | WA | - |
| testcase_18 | WA | - |
| testcase_19 | AC | 2 ms
6,940 KB |
| testcase_20 | AC | 2 ms
6,944 KB |
| testcase_21 | AC | 1 ms
6,940 KB |
| testcase_22 | AC | 2 ms
6,940 KB |
| testcase_23 | AC | 2 ms
6,944 KB |
| testcase_24 | AC | 1 ms
6,944 KB |
| testcase_25 | AC | 2 ms
6,944 KB |
| testcase_26 | AC | 1 ms
6,940 KB |
| testcase_27 | AC | 1 ms
6,940 KB |
| testcase_28 | AC | 1 ms
6,944 KB |
| testcase_29 | AC | 1 ms
6,940 KB |
| testcase_30 | AC | 1 ms
6,940 KB |
コンパイルメッセージ
main.cpp: In function ‘void vizGraph(vvll&, int, std::string)’:
main.cpp:43:425: warning: ignoring return value of ‘int system(const char*)’ declared with attribute ‘warn_unused_result’ [-Wunused-result]
43 | void vizGraph(vvll& g, int mode = 0, string filename = "out.png") { ofstream ofs("./out.dot"); ofs << "digraph graph_name {" << endl; set<P> memo; rep(i, g.size()) rep(j, g[i].size()) { if (mode && (memo.count(P(i, g[i][j])) || memo.count(P(g[i][j], i)))) continue; memo.insert(P(i, g[i][j])); ofs << " " << i << " -> " << g[i][j] << (mode ? " [arrowhead = none]" : "")<< endl; } ofs << "}" << endl; ofs.close(); system(((string)"dot -T png out.dot >" + filename).c_str()); }
| ~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
ソースコード
#include <bits/stdc++.h>
#include <sys/time.h>
using namespace std;
#define rep(i,n) for(long long i = 0; i < (long long)(n); i++)
#define repi(i,a,b) for(long long i = (long long)(a); i < (long long)(b); i++)
#define pb push_back
#define all(x) (x).begin(), (x).end()
#define fi first
#define se second
#define mt make_tuple
#define mp make_pair
#define ZERO(a) memset(a,0,sizeof(a))
template<class T1, class T2> bool chmin(T1 &a, T2 b) { return b < a && (a = b, true); }
template<class T1, class T2> bool chmax(T1 &a, T2 b) { return a < b && (a = b, true); }
#define exists find_if
#define forall all_of
using ll = long long; using vll = vector<ll>; using vvll = vector<vll>; using P = pair<ll, ll>;
using ld = long double; using vld = vector<ld>;
using vi = vector<int>; using vvi = vector<vi>; vll conv(vi& v) { vll r(v.size()); rep(i, v.size()) r[i] = v[i]; return r; }
inline void input(int &v){ v=0;char c=0;int p=1; while(c<'0' || c>'9'){if(c=='-')p=-1;c=getchar();} while(c>='0' && c<='9'){v=(v<<3)+(v<<1)+c-'0';c=getchar();} v*=p; }
template <typename T, typename U> ostream &operator<<(ostream &o, const pair<T, U> &v) { o << "(" << v.first << ", " << v.second << ")"; return o; }
template<size_t...> struct seq{}; template<size_t N, size_t... Is> struct gen_seq : gen_seq<N-1, N-1, Is...>{}; template<size_t... Is> struct gen_seq<0, Is...> : seq<Is...>{};
template<class Ch, class Tr, class Tuple, size_t... Is>
void print_tuple(basic_ostream<Ch,Tr>& os, Tuple const& t, seq<Is...>){ using s = int[]; (void)s{0, (void(os << (Is == 0? "" : ", ") << get<Is>(t)), 0)...}; }
template<class Ch, class Tr, class... Args>
auto operator<<(basic_ostream<Ch, Tr>& os, tuple<Args...> const& t) -> basic_ostream<Ch, Tr>& { os << "("; print_tuple(os, t, gen_seq<sizeof...(Args)>()); return os << ")"; }
ostream &operator<<(ostream &o, const vvll &v) { rep(i, v.size()) { rep(j, v[i].size()) o << v[i][j] << " "; o << endl; } return o; }
template <typename T> ostream &operator<<(ostream &o, const vector<T> &v) { o << '['; rep(i, v.size()) o << v[i] << (i != v.size()-1 ? ", " : ""); o << "]"; return o; }
template <typename T> ostream &operator<<(ostream &o, const set<T> &m) { o << '['; for (auto it = m.begin(); it != m.end(); it++) o << *it << (next(it) != m.end() ? ", " : ""); o << "]"; return o; }
template <typename T> ostream &operator<<(ostream &o, const unordered_set<T> &m) { o << '['; for (auto it = m.begin(); it != m.end(); it++) o << *it << (next(it) != m.end() ? ", " : ""); o << "]"; return o; }
template <typename T, typename U> ostream &operator<<(ostream &o, const map<T, U> &m) { o << '['; for (auto it = m.begin(); it != m.end(); it++) o << *it << (next(it) != m.end() ? ", " : ""); o << "]"; return o; }
template <typename T, typename U, typename V> ostream &operator<<(ostream &o, const unordered_map<T, U, V> &m) { o << '['; for (auto it = m.begin(); it != m.end(); it++) o << *it; o << "]"; return o; }
vector<int> range(const int x, const int y) { vector<int> v(y - x + 1); iota(v.begin(), v.end(), x); return v; }
template <typename T> istream& operator>>(istream& i, vector<T>& o) { rep(j, o.size()) i >> o[j]; return i;}
string bits_to_string(ll input, ll n=64) { string s; rep(i, n) s += '0' + !!(input & (1ll << i)); reverse(all(s)); return s; }
template <typename T> ostream &operator<<(ostream &o, const priority_queue<T> &v) { auto tmp = v; while (tmp.size()) { auto x = tmp.top(); tmp.pop(); o << x << " ";} o << endl; return o; }
template <typename T> unordered_map<T, ll> counter(vector<T> vec){unordered_map<T, ll> ret; for (auto&& x : vec) ret[x]++; return ret;};
string substr(string s, P x) {return s.substr(x.fi, x.se - x.fi); }
void vizGraph(vvll& g, int mode = 0, string filename = "out.png") { ofstream ofs("./out.dot"); ofs << "digraph graph_name {" << endl; set<P> memo; rep(i, g.size()) rep(j, g[i].size()) { if (mode && (memo.count(P(i, g[i][j])) || memo.count(P(g[i][j], i)))) continue; memo.insert(P(i, g[i][j])); ofs << " " << i << " -> " << g[i][j] << (mode ? " [arrowhead = none]" : "")<< endl; } ofs << "}" << endl; ofs.close(); system(((string)"dot -T png out.dot >" + filename).c_str()); }
size_t random_seed; namespace std { using argument_type = P; template<> struct hash<argument_type> { size_t operator()(argument_type const& x) const { size_t seed = random_seed; seed ^= hash<ll>{}(x.fi); seed ^= (hash<ll>{}(x.se) << 1); return seed; } }; }; // hash for various class
namespace myhash{ const int Bsizes[]={3,9,13,17,21,25,29,33,37,41,45,49,53,57,61,65,69,73,77,81}; const int xor_nums[]={0x100007d1,0x5ff049c9,0x14560859,0x07087fef,0x3e277d49,0x4dba1f17,0x709c5988,0x05904258,0x1aa71872,0x238819b3,0x7b002bb7,0x1cf91302,0x0012290a,0x1083576b,0x76473e49,0x3d86295b,0x20536814,0x08634f4d,0x115405e8,0x0e6359f2}; const int hash_key=xor_nums[rand()%20]; const int mod_key=xor_nums[rand()%20]; template <typename T> struct myhash{ std::size_t operator()(const T& val) const { return (hash<T>{}(val)%mod_key)^hash_key; } }; };
template <typename T> class uset:public std::unordered_set<T,myhash::myhash<T>> { using SET=std::unordered_set<T,myhash::myhash<T>>; public: uset():SET(){SET::rehash(myhash::Bsizes[rand()%20]);} };
uint32_t randxor() { static uint32_t x=1+(uint32_t)random_seed,y=362436069,z=521288629,w=88675123; uint32_t t; t=(x^(x<<11));x=y;y=z;z=w; return( w=(w^(w>>19))^(t^(t>>8)) ); }
struct timeval start; double sec() { struct timeval tv; gettimeofday(&tv, NULL); return (tv.tv_sec - start.tv_sec) + (tv.tv_usec - start.tv_usec) * 1e-6; }
struct init_{init_(){ gettimeofday(&start, NULL); ios::sync_with_stdio(false); cin.tie(0); struct timeval myTime; struct tm *time_st; gettimeofday(&myTime, NULL); time_st = localtime(&myTime.tv_sec); srand(myTime.tv_usec); random_seed = RAND_MAX / 2 + rand() / 2; }} init__;
#define rand randxor
static const double EPS = 1e-14;
static const long long INF = 1e18;
static const long long mo = 1e9+7;
#define ldout fixed << setprecision(40)
// https://github.com/togasakih/Togasat
namespace togasat {
using Var = int;
using CRef = int;
using lbool = int;
const CRef CRef_Undef = INT32_MAX;
class Solver {
private:
const lbool l_True = 0;
const lbool l_False = 1;
const lbool l_Undef = 2;
const int var_Undef = -1;
// Literal
struct Lit {
int x;
inline bool operator==(Lit p) const { return x == p.x; }
inline bool operator!=(Lit p) const { return x != p.x; }
inline bool operator<(Lit p) const { return x < p.x; }
inline Lit operator~() {
Lit q;
q.x = x ^ 1;
return q;
}
};
inline Lit mkLit(Var var, bool sign) {
Lit p;
p.x = var + var + sign;
return p;
};
inline bool sign(Lit p) const { return p.x & 1; }
inline int var(Lit p) const { return p.x >> 1; }
inline int toInt(Var v) { return v; }
inline int toInt(Lit p) { return p.x; }
inline Lit toLit(int x) {
Lit p;
p.x = x;
return p;
}
const Lit lit_Undef = {-2};
const Lit lit_Error = {-1};
// lifted boolean
// VarData
struct VarData {
CRef reason;
int level;
};
inline VarData mkVarData(CRef cr, int l) {
VarData d = {cr, l};
return d;
}
// Watcher
struct Watcher {
CRef cref;
Lit blocker;
Watcher() {}
Watcher(CRef cr, Lit p) : cref(cr), blocker(p) {}
bool operator==(const Watcher &w) const { return cref == w.cref; }
bool operator!=(const Watcher &w) const { return cref != w.cref; }
};
// Clause
class Clause {
public:
struct {
bool learnt;
int size;
} header;
std::vector<Lit> data; //(x1 v x2 v not x3)
Clause() {}
Clause(const std::vector<Lit> &ps, bool learnt) {
header.learnt = learnt;
header.size = ps.size();
for (int i = 0; i < ps.size(); i++) {
data.push_back(ps[i]);
}
}
int size() const { return header.size; }
bool learnt() const { return header.learnt; }
Lit &operator[](int i) { return data[i]; }
Lit operator[](int i) const { return data[i]; }
};
CRef alloc_clause(const std::vector<Lit> &ps, bool learnt = false) {
static CRef res = 0;
ca[res] = Clause(ps, learnt);
return res++;
}
Var newVar(bool sign = true, bool dvar = true) {
int v = nVars();
assigns.push_back(l_Undef);
vardata.push_back(mkVarData(CRef_Undef, 0));
activity.push_back(0.0);
seen.push_back(false);
polarity.push_back(sign);
decision.push_back(0);
setDecisionVar(v, dvar);
return v;
}
bool addClause_(std::vector<Lit> &ps) {
std::sort(ps.begin(), ps.end());
// empty clause
if (ps.size() == 0) {
return false;
} else if (ps.size() == 1) {
uncheckedEnqueue(ps[0]);
} else {
CRef cr = alloc_clause(ps, false);
clauses.insert(cr);
attachClause(cr);
}
return true;
}
void attachClause(CRef cr) {
const Clause &c = ca[cr];
assert(c.size() > 1);
watches[(~c[0]).x].push_back(Watcher(cr, c[1]));
watches[(~c[1]).x].push_back(Watcher(cr, c[0]));
}
// Input
void readClause(const std::string &line, std::vector<Lit> &lits) {
lits.clear();
int parsed_lit, var;
parsed_lit = var = 0;
bool neg = false;
std::stringstream ss(line);
while (ss) {
int val;
ss >> val;
if (val == 0)
break;
var = abs(val) - 1;
while (var >= nVars()) {
newVar();
}
lits.push_back(val > 0 ? mkLit(var, false) : mkLit(var, true));
}
}
std::unordered_map<CRef, Clause> ca; // store clauses
std::unordered_set<CRef> clauses; // original problem;
std::unordered_set<CRef> learnts;
std::unordered_map<int, std::vector<Watcher>> watches;
std::vector<VarData> vardata; // store reason and level for each variable
std::vector<bool> polarity; // The preferred polarity of each variable
std::vector<bool> decision;
std::vector<bool> seen;
// Todo
int qhead = 0;
std::vector<Lit> trail;
std::vector<int> trail_lim;
// Todo rename(not heap)
std::set<std::pair<double, Var>> order_heap;
std::vector<double> activity;
double var_inc;
std::vector<Lit> model;
std::vector<Lit> conflict;
int nVars() const { return vardata.size(); }
int decisionLevel() const { return trail_lim.size(); }
void newDecisionLevel() { trail_lim.push_back(trail.size()); }
inline CRef reason(Var x) const { return vardata[x].reason; }
inline int level(Var x) const { return vardata[x].level; }
inline void varBumpActivity(Var v){
std::pair<double, Var> p = std::make_pair(activity[v], v);
activity[v] += var_inc;
if (order_heap.erase(p) == 1){
order_heap.emplace(std::make_pair(activity[v], v));
}
if (activity[v] > 1e100){
//Rescale
std::set<std::pair<double,Var>> tmp_order;
tmp_order = order_heap;
order_heap.clear();
for (int i = 0; i < nVars(); i++){
activity[i] *= 1e-100;
}
for (auto &val : tmp_order){
order_heap.emplace(std::make_pair(activity[val.first], val.first));
}
var_inc *= 1e-100;
}
}
bool satisfied(const Clause &c) const {
for (int i = 0; i < c.size(); i++) {
if (value(c[i]) == l_True) {
return true;
}
}
return false;
}
lbool value(Var p) const { return assigns[p]; }
lbool value(Lit p) const {
if (assigns[var(p)] == l_Undef) {
return l_Undef;
}
return assigns[var(p)] ^ sign(p);
}
void setDecisionVar(Var v, bool b) {
decision[v] = b;
order_heap.emplace(std::make_pair(0.0, v));
}
void uncheckedEnqueue(Lit p, CRef from = CRef_Undef) {
assert(value(p) == l_Undef);
assigns[var(p)] = sign(p);
vardata[var(p)] = mkVarData(from, decisionLevel());
trail.push_back(p);
}
// decision
Lit pickBranchLit() {
Var next = var_Undef;
while (next == var_Undef or value(next) != l_Undef) {
if (order_heap.empty()) {
next = var_Undef;
break;
} else {
auto p = *order_heap.rbegin();
next = p.second;
order_heap.erase(p);
}
}
return next == var_Undef ? lit_Undef : mkLit(next, polarity[next]);
}
// clause learning
void analyze(CRef confl, std::vector<Lit> &out_learnt, int &out_btlevel) {
int pathC = 0;
Lit p = lit_Undef;
int index = trail.size() - 1;
out_learnt.push_back(mkLit(0, false));
do {
assert(confl != CRef_Undef);
Clause &c = ca[confl];
for (int j = (p == lit_Undef) ? 0 : 1; j < c.size(); j++) {
Lit q = c[j];
if (not seen[var(q)] and level(var(q)) > 0) {
varBumpActivity(var(q));
seen[var(q)] = 1;
if (level(var(q)) >= decisionLevel()) {
pathC++;
} else {
out_learnt.push_back(q);
}
}
}
while (not seen[var(trail[index--])])
;
p = trail[index + 1];
confl = reason(var(p));
seen[var(p)] = 0;
pathC--;
} while (pathC > 0);
out_learnt[0] = ~p;
// unit clause
if (out_learnt.size() == 1) {
out_btlevel = 0;
} else {
int max_i = 1;
for (int i = 2; i < out_learnt.size(); i++) {
if (level(var(out_learnt[i])) > level(var(out_learnt[max_i]))) {
max_i = i;
}
}
Lit p = out_learnt[max_i];
out_learnt[max_i] = out_learnt[1];
out_learnt[1] = p;
out_btlevel = level(var(p));
}
for (int i = 0; i < out_learnt.size(); i++) {
seen[var(out_learnt[i])] = false;
}
}
// backtrack
void cancelUntil(int level) {
if (decisionLevel() > level) {
for (int c = trail.size() - 1; c >= trail_lim[level]; c--) {
Var x = var(trail[c]);
assigns[x] = l_Undef;
polarity[x] = sign(trail[c]);
order_heap.emplace(std::make_pair(activity[x], x));
}
qhead = trail_lim[level];
trail.erase(trail.end() - (trail.size() - trail_lim[level]), trail.end());
trail_lim.erase(trail_lim.end() - (trail_lim.size() - level),
trail_lim.end());
}
}
CRef propagate() {
CRef confl = CRef_Undef;
int num_props = 0;
while (qhead < trail.size()) {
Lit p = trail[qhead++]; // 'p' is enqueued fact to propagate.
std::vector<Watcher> &ws = watches[p.x];
std::vector<Watcher>::iterator i, j, end;
num_props++;
for (i = j = ws.begin(), end = i + ws.size(); i != end;) {
// Try to avoid inspecting the clause:
Lit blocker = i->blocker;
if (value(blocker) == l_True) {
*j++ = *i++;
continue;
}
CRef cr = i->cref;
Clause &c = ca[cr];
Lit false_lit = ~p;
if (c[0] == false_lit)
c[0] = c[1], c[1] = false_lit;
assert(c[1] == false_lit);
i++;
Lit first = c[0];
Watcher w = Watcher(cr, first);
if (first != blocker && value(first) == l_True) {
*j++ = w;
continue;
}
// Look for new watch:
for (int k = 2; k < c.size(); k++)
if (value(c[k]) != l_False) {
c[1] = c[k];
c[k] = false_lit;
watches[(~c[1]).x].push_back(w);
goto NextClause;
}
*j++ = w;
if (value(first) == l_False) { // conflict
confl = cr;
qhead = trail.size();
while (i < end)
*j++ = *i++;
} else {
uncheckedEnqueue(first, cr);
}
NextClause:;
}
int size = i - j;
ws.erase(ws.end() - size, ws.end());
}
return confl;
}
static double luby(double y, int x) {
// Find the finite subsequence that contains index 'x', and the
// size of that subsequence:
int size, seq;
for (size = 1, seq = 0; size < x + 1; seq++, size = 2 * size + 1)
;
while (size - 1 != x) {
size = (size - 1) >> 1;
seq--;
x = x % size;
}
return pow(y, seq);
}
lbool search(int nof_conflicts) {
int backtrack_level;
std::vector<Lit> learnt_clause;
learnt_clause.push_back(mkLit(-1, false));
int conflictC = 0;
while (true) {
CRef confl = propagate();
if (confl != CRef_Undef) {
// CONFLICT
conflictC++;
if (decisionLevel() == 0)
return l_False;
learnt_clause.clear();
analyze(confl, learnt_clause, backtrack_level);
cancelUntil(backtrack_level);
if (learnt_clause.size() == 1) {
uncheckedEnqueue(learnt_clause[0]);
} else {
CRef cr = alloc_clause(learnt_clause, true);
learnts.insert(cr);
attachClause(cr);
uncheckedEnqueue(learnt_clause[0], cr);
}
//varDecay
var_inc *= 1.05;
} else {
// NO CONFLICT
if ((nof_conflicts >= 0 and conflictC >= nof_conflicts)) {
cancelUntil(0);
return l_Undef;
}
Lit next = pickBranchLit();
if (next == lit_Undef) {
return l_True;
}
newDecisionLevel();
uncheckedEnqueue(next);
}
}
};
public:
std::vector<lbool> assigns; // The current assignments (ex assigns[0] = 0 ->
// X1 = True, assigns[1] = 1 -> X2 = False)
lbool answer; // SATISFIBLE 0 UNSATISFIBLE 1 UNKNOWN 2
Solver() { }
Solver(int n) { for (int i = 0; i < n; i++) { vector<int> tmp = {i+1, -(i+1)}; addClause(tmp); } }
void parse_dimacs_problem(std::string problem_name) {
std::vector<Lit> lits;
int vars = 0;
int clauses = 0;
std::string line;
std::ifstream ifs(problem_name, std::ios_base::in);
while (ifs.good()) {
getline(ifs, line);
if (line.size() > 0) {
if (line[0] == 'p') {
sscanf(line.c_str(), "p cnf %d %d", &vars, &clauses);
} else if (line[0] == 'c' or line[0] == 'p') {
continue;
} else {
readClause(line, lits);
if (lits.size() > 0)
addClause_(lits);
}
}
}
ifs.close();
}
lbool solve() {
model.clear();
conflict.clear();
lbool status = l_Undef;
answer = l_Undef;
var_inc = 1.01;
int curr_restarts = 0;
double restart_inc = 2;
double restart_first = 100;
while (status == l_Undef) {
double rest_base = luby(restart_inc, curr_restarts);
status = search(rest_base * restart_first);
curr_restarts++;
}
answer = status;
return status;
};
void addClause(std::vector<int> &clause) {
std::vector<Lit> lits;
for (int i = 0; i < clause.size(); i++) {
int var = abs(clause[i]) - 1;
while (var >= nVars())
newVar();
lits.push_back(clause[i] > 0 ? mkLit(var, false) : mkLit(var, true));
}
addClause_(lits);
}
void print_answer() {
if (answer == 0) {
std::cout << "SAT" << std::endl;
for (int i = 0; i < assigns.size(); i++) {
if (assigns[i] == 0) {
std::cout << (i + 1) << " ";
} else {
std::cout << -(i + 1) << " ";
}
}
std::cout << "0" << std::endl;
} else {
std::cout << "UNSAT" << std::endl;
}
}
};
}
class SAT {
public:
int n;
// v in [0, n) x_v = T
// v in [n, 2n) x_v = F
vector<vector<int>> g, g_rev;
vector<bool> ret;
SAT (int n_) : n(n_), g(n*2), g_rev(n*2) { }
inline int node(int t) {
return (t > 0 ? t-1 : n+(-t)-1);
}
// and (sign(t1) x_|t1| or sign(t2) t2)を論理式に加える。
// ただし、sign(t)はt>0で何もなし、t<0でnot
//
// 1 <= |t1| <= n
// 1 <= |t2| <= n
void addClause(int t1, int t2) {
assert(1 <= abs(t1) && abs(t1) <= n);
assert(1 <= abs(t2) && abs(t2) <= n);
g[node(-t1)].pb(node(t2));
g[node(-t2)].pb(node(t1));
g_rev[node(t1)].pb(node(-t2));
g_rev[node(t2)].pb(node(-t1));
}
// 従属可能で1を出力
bool isSAT(void) {
// SCC
vector<int> color(g.size(), -1); // color[i] == color[j]ならばiとjは同じ連結成分
{
vector<int> id;
vector<bool> visited(g.size());
rep(i, g.size()) {
function<void(int)> dfs1 = [&](int v) {
if (visited[v]) return;
visited[v] = true;
for (auto x : g[v]) dfs1(x);
id.pb(v);
};
dfs1(i);
}
fill(all(visited), false);
for (int i = id.size() - 1; i >= 0; i--) {
function<void(int)> dfs2 = [&](int v) {
if (visited[v]) return;
visited[v] = true;
for (auto x : g_rev[v]) dfs2(x);
color[v] = i;
};
dfs2(id[i]);
}
}
ret.resize(0);
rep(v, n) if (color[v] == color[v+n]) return 0;
ret.resize(n);
rep(i, n) ret[i] = color[i] > color[i+n];
return 1;
}
// 解ありの場合、x_i = ret[i]がSATを与える。
// 解なしの場合、ret.size() == 0である
vector<bool> getAnswer(void) { return ret; }
void print_answer(void) {
if (ret.size()) {
cout << "SAT : "; rep(i, n) cout << ret[i] << " "; cout << endl;
} else {
cout << "UNSAT" << endl;
}
}
};
int main(void) {
ll n; cin >> n;
if (n > 26*2) return cout << "Impossible" << endl, 0;
vector<string> u(n); cin >> u;
SAT sat(n);
map<string, vll> memo;
rep(i, n) {
memo[u[i].substr(0, 1)].pb(i+1);
memo[u[i].substr(1, 2)].pb(i+1);
memo[u[i].substr(0, 2)].pb(-i-1);
memo[u[i].substr(2, 1)].pb(-i-1);
}
for (auto&& x : memo) {
auto&& v = x.se;
for (auto i : v) for (auto j : v) if (i != j) {
sat.addClause(-i, -j);
}
}
ll ret = sat.isSAT();
if (ret) {
rep(i, n) {
if (sat.ret[i] != 0)
cout << u[i].substr(0, 1) << " " << u[i].substr(1, 2) << endl;
else
cout << u[i].substr(0, 2) << " " << u[i].substr(2, 1) << endl;
}
} else {
cout << "Impossible" << endl;
}
}