MOD = 1000000007 # 扩展欧几里得算法 def extended_gcd(a, b): if a == 0: return (b, 0, 1) else: g, y, x = extended_gcd(b % a, a) return (g, x - (b // a) * y, y) def mod_inverse(p, q): g, x, _ = extended_gcd(p, q) if g != 1: raise ValueError(f"{p} 和 {q} 不互质,无法找到模逆元") else: # 确保结果是正数 inverse = x % q r...