Give it an input and say what you think comes back. It compiles and runs for real, so a wrong guess still shows you the answer — probe as much as you like. Only correct predictions count.
Locked until you have predicted 4 outputs correctly.
| 1 | int countFrom(const string& s, int i, vector<int>& memo) { |
| 2 | int n = s.size(); |
| 3 | if (i == n) return 1; |
| 4 | if (s[i] == '0') return 0; |
| 5 | if (memo[i] != -1) return memo[i]; |
| 6 | |
| 7 | int total = countFrom(s, i + 1, memo); |
| 8 | if (i + 1 < n) { |
| 9 | int two = (s[i] - '0') * 10 + (s[i + 1] - '0'); |
| 10 | if (two <= 26) { |
| 11 | total += countFrom(s, i + 2, memo); |
| 12 | } |
| 13 | } |
| 14 | memo[i] = total; |
| 15 | return total; |
| 16 | } |
| 17 | |
| 18 | int solution(const string& s) { |
| 19 | if (s.empty()) return 0; |
| 20 | vector<int> memo(s.size(), -1); |
| 21 | return countFrom(s, 0, memo); |
| 22 | } |
Names have been stripped. The signature is the only clue you get for free. Compiled as C++20 with the standard headers and using namespace std; already in scope.