1309. Decrypt String from Alphabet to Integer Mapping ---E

Q:

Given a string s formed by digits ('0' - '9') and '#' . We want to map s to English lowercase characters as follows:

• Characters ('a' to 'i') are represented by ('1' to '9') respectively.
• Characters ('j' to 'z') are represented by ('10#' to '26#') respectively. 

Return the string formed after mapping.

It's guaranteed that a unique mapping will always exist.

 

Example 1:

Input: s = "10#11#12"
Output: "jkab"
Explanation: "j" -> "10#" , "k" -> "11#" , "a" -> "1" , "b" -> "2".

Example 2:

Input: s = "1326#"
Output: "acz"

Example 3:

Input: s = "25#"
Output: "y"

Example 4:

Input: s = "12345678910#11#12#13#14#15#16#17#18#19#20#21#22#23#24#25#26#"
Output: "abcdefghijklmnopqrstuvwxyz"

 

Constraints:

• 1 <= s.length <= 1000
• s[i] only contains digits letters ('0'-'9') and '#' letter.
• s will be valid string such that mapping is always possible.

A:

class Solution {
public:
    string freqAlphabets(string s) {
        vector<char> V;
        int n = s.length();
        for(int i =0;i<n; ++i){
            char val = 'a';// this value is never used though
            if(i+2<n && s[i+2] == '#'){
                val = 'j' + stoi(s.substr(i,2)) - 10;
                i+=2;
            }else{
                val = 'a' + (s[i] - '1');
            }
            V.push_back(val);
        }
        string res(V.begin(), V.end());
        return res;
    }
};