#include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include using namespace std; using namespace atcoder; typedef long long ll; #define rep(i, n) for (int i = 0; i < (int)(n); i++) #define repr(i, n) for (int i = (int)(n) - 1; i >= 0; i--) #define repk(i, k, n) for (int i = k; i < (int)(n); i++) #define all(v) v.begin(), v.end() #define mod1 1000000007 #define mod2 998244353 #define mod3 100000007 #define vi vector #define vs vector #define vc vector #define vl vector #define vb vector #define vvi vector> #define vvc vector> #define vvl vector> #define vvb vector> #define vvvi vector>> #define vvvl vector>> #define pii pair #define pil pair #define pli pair #define pll pair #define vpii vector> #define vpll vector> #define vvpii vector>> #define vvpll vector>> // using mint = modint998244353; template void debug(T e) { cerr << e << endl; } template void debug(vector &v) { rep(i, v.size()) { cerr << v[i] << " "; } cerr << endl; } template void debug(vector> &v) { rep(i, v.size()) { rep(j, v[i].size()) { cerr << v[i][j] << " "; } cerr << endl; } } template void debug(vector> &v) { rep(i, v.size()) { cerr << v[i].first << " " << v[i].second << endl; } } template void debug(set &st) { for (auto itr = st.begin(); itr != st.end(); itr++) { cerr << *itr << " "; } cerr << endl; } template void debug(multiset &ms) { for (auto itr = ms.begin(); itr != ms.end(); itr++) { cerr << *itr << " "; } cerr << endl; } template void debug(map &mp) { for (auto itr = mp.begin(); itr != mp.end(); itr++) { cerr << itr->first << " " << itr->second << endl; } } void debug_out() { cerr << endl; } template void debug_out(Head H, Tail... T) { cerr << H << " "; debug_out(T...); } using mint = modint998244353; bool issame(vector &A, vector &B, vector &C, ll i, ll j) { // true なら同じ向き,false なら違う向き if (A[i] == A[j] && B[i] == B[j]) { return false; } else if (A[i] == A[j] && B[i] == C[j]) { return true; } else if (A[i] == A[j] && C[i] == B[j]) { return true; } else if (A[i] == A[j] && C[i] == C[j]) { return false; } else if (A[i] == B[j] && B[i] == C[j]) { return false; } else if (A[i] == B[j] && C[i] == C[j]) { return true; } else if (B[i] == A[j] && C[i] == B[j]) { return false; } else if (B[i] == A[j] && C[i] == C[j]) { return true; } return false; } int main() { ll M; cin >> M; vector A(M); vector B(M); vector C(M); for (ll i = 0; i < M; i++) { cin >> A[i] >> B[i] >> C[i]; } map, vector> mp; for (ll i = 0; i < M; i++) { mp[make_pair(A[i], B[i])].push_back(i); mp[make_pair(A[i], C[i])].push_back(i); mp[make_pair(B[i], C[i])].push_back(i); } vector> graph(M, vector(0)); for (auto itr = mp.begin(); itr != mp.end(); itr++) { if ((itr->second).size() > 2) { cout << "NO" << endl; return 0; } else if ((itr->second).size() == 2) { ll v1 = (itr->second)[0]; ll v2 = (itr->second)[1]; graph[v1].push_back(v2); graph[v2].push_back(v1); } } // debug(graph); // 二部グラフ判定 // 「単純な二部グラフ」というわけではなさそうである vector col(M, -1); queue que; for (ll i = 0; i < M; i++) { if (col[i] != -1) { continue; } col[i] = 0; que.push(i); while (que.size()) { ll p = que.front(); que.pop(); for (ll x : graph[p]) { if (col[x] != -1) { if (issame(A, B, C, x, p)) { if (col[x] != col[p]) { cout << "NO" << endl; return 0; } } else { if (col[x] == col[p]) { cout << "NO" << endl; // debug(col); return 0; } } continue; } if (issame(A, B, C, x, p)) { col[x] = col[p]; } else { col[x] = 1 - col[p]; } que.push(x); } } } cout << "YES" << endl; }