#include<bits/stdc++.h>
using namespace std;
int n, m, res, sg, out[35];
bool lt[35][35];
pair <int, int> P[3333];
void clear() {
    memset(lt, 0, sizeof(lt));
}
void floyd() {
    for(int k=1; k<=n; k++)
        for(int i=1; i<=n; i++)
            for(int j=1; j<=n; j++) {
                lt[i][j] |= lt[i][k] & lt[k][j];
            }
}
int check(int t) {
    memset(lt, 0, sizeof(lt));
    for(int i=1; i<=t; i++) {
        lt[P[i].first][P[i].second] = 1;
    }
    floyd();
    // if(t == 6) {
    //     cout << "  ";
    //     for(int i=1; i<=n; i++)
    //         cout << (char)(i^'@') << ' ';
    //     cout << endl;
    //     for(int i=1; i<=n; i++) {
    //         cout << (char)(i^'@') << ' ';
    //         for(int j=1; j<=n; j++) {
    //             cout << lt[i][j] << ' ';
    //         }
    //         cout << endl;
    //     }
    // }
    int chk = 1;
    for(int i=1; i<=n; i++) {
        if(lt[i][i]) {
            chk = -1;
            goto EEEE;
        }
        for(int j=1; j<i; j++) {
            if(lt[i][j] ^ lt[j][i]) continue;
            else if(lt[i][j]) {
                chk = -1;
                goto EEEE;
            } else if(chk > 0) {
                chk = 0;
            }
        }
    }
    EEEE: return chk;
}
void solve() {
    res = m+1;
    sg = 0;
    for(int i=1; i<=m; i++) {
        char x, y, z;
        cin >> x >> z >> y;
        P[i] = {x^'@', y^'@'};
        int w = check(i);
        if(w && !sg) {
            res = i; sg = w;
        }
    }
    res *= sg;
    return ;
}
void print() {
    if(res > 0) {
        cout << "Sorted sequence determined after " << res << " relations: ";
        iota(out+1, out+n+1, 1ll);
        sort(out+1, out+n+1, [](int x, int y) { return lt[x][y]; });
        for(int i=1; i<=n; i++) cout << (char)(out[i]^'@');
        cout << ".\n";
    }
    else if(res < 0) {
        cout << "Inconsistency found after " << -res << " relations.\n";
    }
    else cout << "Sorted sequence cannot be determined.\n";
}
signed main() {
    ios_base :: sync_with_stdio(0);
    cin.tie(0); cout.tie(0);
    while(cin >> n >> m && n+m) {
        clear();
        solve();
        print();
    }
}

这份代码下面数据输出

Sorted sequence determined after 25 relations: AZYXWVUTSRQPONMLKJIHGFEDCB.

但正确的是

Sorted sequence determined after 25 relations: ABCDEFGHIJKLMNOPQRSTUVWXYZ.

数据：

26 26
A<B
B<C
C<D
D<E
E<F
F<G
G<H
H<I
I<J
J<K
K<L
L<M
M<N
N<O
O<P
P<Q
Q<R
R<S
S<T
T<U
U<V
V<W
W<X
X<Y
Y<Z
Z<A