#include <bits/stdc++.h>
using namespace std;
#define pb push_back
#define pf push_front
#define mp make_pair
#define fi first
#define se second
#define int long long
#define all(x) (x).begin(), (x).end()
typedef long double ld;
typedef long long ll;
typedef pair<ll,ll> pll;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<bool> vb;
typedef vector<vector<int>> vvi;
typedef vector<vector<bool>> vvb;
typedef vector<vector<ll>> vvll;
typedef vector<string> vs;
typedef vector<vector<string>> vvs;
typedef vector<char> vc;
typedef vector<vector<char>> vvc;
typedef map<int, int> mii;
typedef unordered_map<int, int> umii;
const int mod = 1e9 + 7;
const int inf = INTMAX_MAX;
const bool tc = false;
int n, t;
const int mxn = 2e5 + 1;
int s[mxn], e[mxn], nxt[mxn], v[mxn], prv[mxn];
int ans = 1e18;
int cnode = -1;
void dfs(int i) {
v[i] = 1;
if (nxt[i] != 0) {
if (v[nxt[i]] == 1) {
prv[nxt[i]] = i;
cnode = i;
return;
}
if (v[nxt[i]] == 2) return;
assert(v[nxt[i]] != 2);
//cout << nxt[i] << " " << i << '\n';
prv[nxt[i]] = i;
dfs(nxt[i]);
}
v[i] = 2;
}
void cycle(int i) {
cnode = -1;
dfs(i);
if (cnode != -1) {
int node = prv[cnode];
int l = 1;
while (node != cnode) {
//if (node == 0) return;
assert(node != 0);
assert(cnode != 0);
l++;
node = prv[node];
}
ans = min(ans, l);
}
}
// size of smallest cycle
inline void solve() {
int n, t; cin >> n >> t; set<int> x;
for (int i = 1; i <= n; i++) cin >> s[i] >> e[i];
// find parent
for (int i = 1; i <= n; i++) {
pii mx = {-1e18, 0};
for (int j = 1; j <= n; j++) {
if (i == j) continue;
// int si = s[i], ei = e[i] + (s[i] > e[i]) * t, sj = s[j], ej = e[j] + (s[j] > e[j]) * t;
// //cout << si << " " << ei << " " << sj << " " << ej << '\n';
// if (si <= sj && sj <= ei) mx = max(mx, {ej, j});
bool ok = false;
if (s[i] > e[i]) {
if (s[j] > e[j]) {
// j bad, i bad
if (s[j] >= s[i] || s[j] <= e[i] + 1) ok = true;
} else {
// j good, i bad
if (s[j] >= s[i] || s[j] <= e[i] + 1) ok = true;
}
} else {
// ts normal
if (s[j] > e[j]) {
// j bad
if (s[j] >= s[i] && s[j] <= e[i] + 1) ok = true;
} else {
// j good
if (s[j] >= s[i] && s[j] <= e[i] + 1) ok = true;
}
if (e[i] == t - 1 && s[j] == 0) ok = true;
}
if (ok) mx = max(mx, {e[j] + (s[j] > e[j]) * t, j});
}
nxt[i] = mx.se;
//cout << nxt[i] << " ";
}
//cout << '\n';
for (int i = 1; i <= n; i++) {
if (!v[i]) cycle(i);
}
// for (int i = 1; i <= n; i++) cout << prv[i] << " ";
// cout << '\n';
cout << (ans != 1e18 ? ans : -1) << '\n';
}
void setIO(string s) {
freopen((s + ".in").c_str(), "r", stdin);
freopen((s + ".out").c_str(), "w", stdout);
}
signed main() {
ios::sync_with_stdio(false);
cout.tie(0);
cin.tie(0);
//setIO();
int t = 1;
if (tc) {
cin >> t;
}
while (t--) {
solve();
}
}
컴파일 시 표준 에러 (stderr) 메시지
Main.cpp: In function 'void setIO(std::string)':
Main.cpp:129:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
129 | freopen((s + ".in").c_str(), "r", stdin);
| ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Main.cpp:130:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
130 | freopen((s + ".out").c_str(), "w", stdout);
| ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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