# | Time | Username | Problem | Language | Result | Execution time | Memory |
---|---|---|---|---|---|---|---|
1201575 | adiyer | Game (APIO22_game) | C++20 | 0 ms | 0 KiB |
#include <bits/stdc++.h>
using namespace std;
const int MAXN = 5e5 + 11;
int n, k, ok;
int was[MAXN][2];
vector < int > g[MAXN][2];
void dfs(int v, bool t){
was[v][t] = 1;
for(int u : g[v][t])
if(!was[u][t])
dfs(u, t);
}
void init(int _n, int _k) {
n = _n, k = _k;
for(int i = 0; i < k - 1; i++) g[i][0].push_back(i + 1), g[i + 1][1].push_back(i);
dfs(0, 0);
}
int add_teleporter(int u, int v){
g[u][0].push_back(v);
if(was[u][0]) dfs(u, 0);
g[v][1].push_back(u);
for(int i = 0; i < n; i++) was[i][1] = 0;
dfs(u, 1);
if(was[v][0] && was[v][1]) return 1;
return 0;
}
namespace {
int read_int() {
int x;
if (scanf("%d", &x) != 1) {
fprintf(stderr, "Error while reading input\n");
exit(1);
}
return x;
}
} // namespace
int main() {
int N = read_int();
int M = read_int();
int K = read_int();
std::vector<int> u(M), v(M);
for (int i = 0; i < M; ++i) {
u[i] = read_int();
v[i] = read_int();
}
init(N, K);
int i;
for (i = 0; i < M; ++i) {
int answer = add_teleporter(u[i], v[i]);
if (answer != 0 && answer != 1) {
i = -1;
break;
} else if (answer == 1) {
break;
}
}
printf("%d\n", i);
return 0;
}