17. Letter Combinations of a Phone Number | LeetCode Solution
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 digit 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']
.
The solution to the above question is -
class Solution
{
public:
vector<string> ans;
vector<string> letters = {"abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};
void helper(string &s, int i, string t)
{
if (i == s.length())
{
ans.push_back(t);
return;
}
for (auto c : letters[s[i] - '2'])
{
helper(s, i + 1, t + c);
}
}
vector<string> letterCombinations(string digits)
{
if (digits == "")
return ans;
helper(digits, 0, "");
return ans;
}
};
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