LeetCode-in-All
17. Letter Combinations of a Phone Number
Medium
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 <= 4digits[i]is a digit in the range['2', '9'].
Solution
func letterCombinations(digits string) []string {
if len(digits) == 0 {
return nil
}
letters := []string{"", "", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"}
var ans []string
var sb string
findCombinations(0, digits, letters, &sb, &ans)
return ans
}
func findCombinations(start int, nums string, letters []string, curr *string, ans *[]string) {
if len(*curr) == len(nums) {
*ans = append(*ans, *curr)
return
}
for i := start; i < len(nums); i++ {
n := int(nums[i] - '0')
for j := 0; j < len(letters[n]); j++ {
ch := letters[n][j]
*curr += string(ch)
findCombinations(i+1, nums, letters, curr, ans)
*curr = (*curr)[:len(*curr)-1]
}
}
}