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OI-codes/S2OJ/1909/1909.cpp

97 lines
1.6 KiB
C++

#include <iostream>
#include <vector>
using std::cin;
using std::cout;
const char endl = '\n';
const int N = 2005;
int n, a[N][N];
int gauss() {
int c, r;
for (c = r = 1; c <= n; c++) {
int t = r;
for (int i = r; i <= n; i++) {
if (a[i][c]) t = i;
}
if (!a[t][c]) continue;
std::swap(a[t], a[r]);
for (int i = r + 1; i <= n; i++) {
if (a[i][c]) {
for (int j = n + 1; j >= c; j--) {
a[i][j] ^= a[r][j];
}
}
}
r++;
}
if (r <= n) {
for (int i = r; i <= n; i++) {
if (a[i][n + 1]) {
return -1;
}
}
}
for (int i = n; i; i--) {
for (int j = i + 1; j <= n; j++) {
a[i][n + 1] ^= a[i][j] & a[j][n + 1];
}
}
return 0;
}
int main() {
std::ios::sync_with_stdio(false);
cin.tie(nullptr);
cin >> n;
for (int i = 1, k; i <= n; i++) {
cin >> k;
for (int j = 1, x; j <= k; j++) {
cin >> x;
a[i][x] = 1;
}
if (k % 2) {
a[i][i] = 1;
a[i][n + 1] = 1;
}
}
if (gauss() != 0) {
cout << -1 << endl;
} else {
std::vector<int> ans;
for (int i = 1; i <= n; i++) {
if (a[i][n + 1]) {
ans.push_back(i);
}
}
cout << ans.size() << endl;
for (int x : ans) {
cout << x << ' ';
}
cout << endl;
}
return 0;
}