POJ 3905 Perfect Election
思路：非常裸的2-sat，就依据题意建边就可以
代码：
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <vector>
#include <algorithm>
using namespace std; const int MAXNODE = 2005; struct TwoSet {
int n;
vector<int> g[MAXNODE * 2];
bool mark[MAXNODE * 2];
int S[MAXNODE * 2], sn; void init(int tot) {
n = tot * 2;
for (int i = 0; i < n; i += 2) {
g[i].clear();
g[i^1].clear();
}
memset(mark, false, sizeof(mark));
} void add_Edge(int u, int uval, int v, int vval) {
u = u * 2 + uval;
v = v * 2 + vval;
g[u^1].push_back(v);
g[v^1].push_back(u);
} void delete_Edge(int u, int uval, int v, int vval) {
u = u * 2 + uval;
v = v * 2 + vval;
g[u^1].pop_back();
g[v^1].pop_back();
} bool dfs(int u) {
if (mark[u^1]) return false;
if (mark[u]) return true;
mark[u] = true;
S[sn++] = u;
for (int i = 0; i < g[u].size(); i++) {
int v = g[u][i];
if (!dfs(v)) return false;
}
return true;
} bool solve() {
for (int i = 0; i < n; i += 2) {
if (!mark[i] && !mark[i + 1]) {
sn = 0;
if (!dfs(i)){
for (int j = 0; j < sn; j++)
mark[S[j]] = false;
sn = 0;
if (!dfs(i + 1)) return false;
}
}
}
return true;
}
} gao; int n, m; int main() {
while (~scanf("%d%d", &n, &m)) {
gao.init(n);
int u, v;
while (m--) {
scanf("%d%d", &u, &v);
if (u > 0 && v > 0) {
u--; v--;
gao.add_Edge(u, 1, v, 1);
} else if (u > 0 && v < 0) {
v = -v;
u--; v--;
gao.add_Edge(u, 1, v, 0);
} else if (u < 0 && v > 0) {
u = -u;
u--; v--;
gao.add_Edge(u, 0, v, 1);
} else if (u < 0 && v < 0) {
u = -u; v = -v;
u--; v--;
gao.add_Edge(u, 0, v, 0);
}
}
printf("%d\n", gao.solve());
}
return 0;
}