Today I have done leetcode's August LeetCoding Challenge with cpp.

August LeetCoding Challenge 3

Description

Letter Combinations of a Phone Number

Given a string containing digits from 2-9 inclusive, return all possible letter combinations that the number could represent. Return the answer in any order.

A mapping of digits to letters (just like on the telephone buttons) is given below. Note that 1 does not map to any letters.

Example 1:

Input: digits = "23"
Output: ["ad","ae","af","bd","be","bf","cd","ce","cf"]

Example 2:

Input: digits = ""
Output: []

Example 3:

Input: digits = "2"
Output: ["a","b","c"]

Constraints:

• 0 <= digits.length <= 4
• digits[i] is a digit in the range ['2', '9'].

Solution

auto speedup = [](){
  cin.tie(nullptr);
  cout.tie(nullptr);
  ios::sync_with_stdio(false);
  return 0;
}();
class Solution {
public:
  vector<string> letterCombinations(string digits) {
    if(digits.empty()) return vector<string>();
    vector<string> mp = {"abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};
    vector<string> nxt;
    vector<string> current{""};
    for(auto c : digits) {
      for(auto &s : current) {
        for(auto letter : mp[c-'2']) {
          nxt.push_back(s+letter);
        }
      }
      current = nxt;
      nxt.clear();
    }
    return current;
  }
};

// Accepted
// 25/25 cases passed (0 ms)
// Your runtime beats 100 % of cpp submissions
// Your memory usage beats 18.76 % of cpp submissions (6.6 MB)