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 3 outputs correctly.
| 1 | void build(const string& digits, int i, string& current, |
| 2 | vector<string>& out) { |
| 3 | string keys[10] = {"", "", "abc", "def", "ghi", |
| 4 | "jkl", "mno", "pqrs", "tuv", "wxyz"}; |
| 5 | int n = digits.size(); |
| 6 | if (i == n) { |
| 7 | out.push_back(current); |
| 8 | return; |
| 9 | } |
| 10 | |
| 11 | for (char ch : keys[digits[i] - '0']) { |
| 12 | current.push_back(ch); |
| 13 | build(digits, i + 1, current, out); |
| 14 | current.pop_back(); |
| 15 | } |
| 16 | } |
| 17 | |
| 18 | vector<string> solution(const string& digits) { |
| 19 | vector<string> out; |
| 20 | if (digits.empty()) return out; |
| 21 | string current; |
| 22 | build(digits, 0, current, out); |
| 23 | return out; |
| 24 | } |
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.