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Cod sursa(job #382601)
Utilizator |
Marius Stroe Marius |
Data |
14 ianuarie 2010 06:43:47 |
Problema |
2SAT |
Scor |
Ascuns |
Compilator |
cpp |
Status |
done |
Runda |
|
Marime |
3.78 kb |
#include <iostream>
#include <fstream>
#include <vector>
#include <queue>
#include <algorithm>
#include <cassert>
using namespace std;
const char iname[] = "2sat.in";
const char oname[] = "2sat.out";
#define MAX_N 200005
int variables, expressions;
vector <int> var_adj[MAX_N], var_adj_t[MAX_N], vtc(MAX_N), value(MAX_N, -1), scc_in_deg(MAX_N, 0);
vector < vector <int> > sccs;
inline int abs(const int x) {
return (x < 0) ? -x : +x;
}
inline int idx(const int x) {
return (x < 0) ? abs(x) + variables : x;
}
inline int non(const int x) {
return (x > variables) ? x - variables : x + variables;
}
void DFP(int n, vector <int>& used, vector <int>& discover) {
vector <int>::iterator it;
used[n] = 1;
for (it = var_adj[n].begin(); it != var_adj[n].end(); ++ it)
if (!used[*it])
DFP(*it, used, discover);
discover.push_back(n);
}
void DFM(int n, vector <int>& used, vector <int>& scc) {
vector <int>::iterator it;
used[n] = 1;
scc.push_back(n);
for (it = var_adj_t[n].begin(); it != var_adj_t[n].end(); ++ it)
if (!used[*it])
DFM(*it, used, scc);
}
void compute_sccs(void) {
vector <int> used(MAX_N), discover, scc;
used.assign(used.size(), 0);
for (int i = 1; i <= variables * 2; ++ i)
if (!used[i])
DFP(i, used, discover);
used.assign(used.size(), 0);
vector <int>::reverse_iterator it;
for (it = discover.rbegin(); it != discover.rend(); ++ it) {
if (!used[*it]) {
scc.clear();
DFM(*it, used, scc);
for (vector <int>::iterator it2 = scc.begin(); it2 != scc.end(); ++ it2)
vtc[*it2] = sccs.size();
sccs.push_back(scc);
}
}
}
int main(void) {
ifstream in(iname);
assert(in >> variables >> expressions);
assert(1 <= variables && variables <= 100000);
assert(1 <= expressions && expressions <= 200000);
for (int i = 0; i < expressions; ++ i) {
int x, y;
assert(in >> x >> y);
assert(1 <= abs(x) && abs(x) <= variables);
assert(1 <= abs(y) && abs(y) <= variables);
var_adj[non(idx(x))].push_back(idx(y));
var_adj_t[idx(y)].push_back(non(idx(x)));
var_adj[non(idx(y))].push_back(idx(x));
var_adj_t[idx(x)].push_back(non(idx(y)));
}
in.close();
compute_sccs();
int impossible = false;
for (int x = 1; x <= variables; ++ x) {
if (vtc[x] == vtc[x + variables])
impossible = true;
}
ofstream out(oname);
if (!impossible) {
for (int x = 1; x <= variables * 2; ++ x) {
vector <int>::iterator it;
for (it = var_adj[x].begin(); it != var_adj[x].end(); ++ it)
if (vtc[x] != vtc[*it])
scc_in_deg[ vtc[*it] ] ++;
}
queue <int> Q;
for (int idx = 0; idx < (int) sccs.size(); ++ idx) {
if (scc_in_deg[idx] == 0)
Q.push(idx);
}
while (!Q.empty()) {
int idx = Q.front();
Q.pop();
vector <int>::iterator it, i, j;
for (it = sccs[idx].begin(); it != sccs[idx].end(); ++ it) {
int x = (*it > variables) ? *it - variables : *it;
if (value[x] == -1)
value[x] = (*it <= variables) ? 0 : 1;
}
for (i = sccs[idx].begin(); i != sccs[idx].end(); ++ i) {
for (j = var_adj[*i].begin(); j != var_adj[*i].end(); ++ j)
if (vtc[*i] != vtc[*j]) {
if ((-- scc_in_deg[ vtc[*j] ]) == 0)
Q.push(vtc[*j]);
}
}
}
for (int i = 1; i <= variables; ++ i)
out << value[i] << " ";
}
else
out << -1;
out.close();
return 0;
}