Leetcode 17 Letter Combinations of a Phone Number, leetcode

Leetcode 17 Letter Combinations of a Phone Number, leetcode

Given a digit string, return all possible letter combinations that the number coshould represent.

A mapping of digit to letters (just like on the telephone buttons) is given below.

Input:Digit string "23"Output: ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].

Cycle: Enter the number of digits {each character string consisting of the previous + {each letter corresponding to the entered number }}

def letter_combinations(digits)  letter = ['','','abc','def','ghi','jkl','mno','pqrs','tuv','wxyz']  return [] if digits == ''  ans = [['']]  digits.chars.each do |x|    ans << []    ans[-2].each do |y|      letter[x.to_i].chars.each {|c| ans[-1] << y+c}    end  end  ans[-1]end

Recursion: records the currently generated string

def letter_combinations(digits)  @letter = ['','','abc','def','ghi','jkl','mno','pqrs','tuv','wxyz']  return [] if digits == ''  @ans = []  comb('',digits,0)  @ansenddef comb(str,digits,i)  @ans << str if str.length == digits.length  @letter[digits[i].to_i].chars.each {|x| comb(str+x,digits,i+1)}end