classSolution { public: intcrackNumber(int ciphertext){ string s = to_string(ciphertext); int n = s.size(); s = "0" + s; int a = 1, b = 1; for (int i = 2; i <= n; ++i) { int res = a; int x = (s[i] - '0'), y = (s[i - 1] - '0') * 10, z = x + y; if (z != x && z >= 0 && z <= 25) res += b; b = a, a = res; } return a; } };