[JS] Letter Combinations of a Phone Number

🔒 문제 (LeetCode 17)

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.

Constraints:

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

 

🌊 입출력

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"]

 

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🔑 해결

🌌 알고리즘 - DFS

/**
 * @param {string} digits
 * @return {string[]}
 */
var letterCombinations = function(digits) {
    if(digits === null || digits.length === 0) return []
    
    const buttons = ['', '', 'abc', 'def', 'ghi', 'jkl', 'mno', 'pqrs', 'tuv', 'wxyz']
    const result = []
    
    const dfs = (str, idx) => {
        if(idx === digits.length) {
            result.push(str)
            return
        }
        
        for(const letter of buttons[digits[idx]]) {
            dfs(str + letter, idx + 1)
        }
    }
    
    dfs('', 0)

    
    return result
};