暴力递归真的没希望吗？ def rabit ( x ) : if x <= 1 : return 1,0 else : if ( x in dic1 ) : return dic1[x] m , n = rabit ( x - 1 ) dic1[x] = ( m + n , m) return m + n , m n = int ( input() ) dic1 = {} ans = rabit( n )[0] ans %= 1000000000 + 7 print(ans)