<Solution> 17.Letter Combinations of a Phone Number

<Leetcode Solution>

17.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"]

 

Constraints:

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

 

class Solution {
public:
    vector<string> letterCombinations(string digits) {
        if(digits.size() == 0){
            return;
        }
        
        map<char,string> m;
        m['2'] = "abc";
        m['3'] = "def";
        m['4'] = "ghi";
        m['5'] = "jkl";
        m['6'] = "mno";
        m['7'] = "pqrs";
        m['8'] = "tuv";
        m['9'] = "wxyz";
        
        int size = 1;
        
        for(int i=0; i<digits.size(); i++){
            size*=m[digits[i]].size();
        }
        
        
        int itr = size;
        vector<string> ans(size,"");
        
        for(int i=0; i<digits.size(); i++){
            int temp = i,k=0, count=0;
            itr /= m[digits[i]].size();
            
            if(itr == 0){
                itr = 1;
            }
            
            for(int j=0; j<size; j++){
                if(count == itr){
                    k++;
                    if(k == m[digits[i]].size()) {
                        k = 0;
                    }
                    count = 0;
                }
                ans[j] += m[digits[i]][k];
                count++;
            }
        }
        return ans;
    }
};