Formatted question description: https://leetcode.ca/all/1309.html

1309. Decrypt String from Alphabet to Integer Mapping (Easy)

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.

Related Topics:
String

Solution 1.

// OJ: https://leetcode.com/problems/decrypt-string-from-alphabet-to-integer-mapping/
// Time: O(N)
// Space: O(1)
class Solution {
public:
    string freqAlphabets(string s) {
        string ans;
        for (int i = 0, N = s.size(); i < N; ++i) {
            if (i + 2 < N && s[i + 2] == '#') {
                ans += 'a' + (s[i] - '0') * 10 + (s[i + 1] - '0') - 1;
                i += 2;
            } else ans += 'a' + s[i] - '0' - 1;
        }
        return ans;
    }
};

Java

  • class Solution {
        public String freqAlphabets(String s) {
            Stack<Character> stack = new Stack<Character>();
            int length = s.length();
            int index = length - 1;
            while (index >= 0) {
                char c = s.charAt(index);
                if (c == '#') {
                    int num = Integer.parseInt(s.substring(index - 2, index));
                    char letter = (char) (num - 1 + 'a');
                    stack.push(letter);
                    index -= 3;
                } else {
                    char letter = (char) (c - '1' + 'a');
                    stack.push(letter);
                    index--;
                }
            }
            StringBuffer sb = new StringBuffer();
            while (!stack.isEmpty())
                sb.append(stack.pop());
            return sb.toString();
        }
    }
    
  • // OJ: https://leetcode.com/problems/decrypt-string-from-alphabet-to-integer-mapping/
    // Time: O(N)
    // Space: O(1)
    class Solution {
    public:
        string freqAlphabets(string s) {
            string ans;
            for (int i = 0, N = s.size(); i < N; ++i) {
                if (i + 2 < N && s[i + 2] == '#') {
                    ans += 'a' + (s[i] - '0') * 10 + (s[i + 1] - '0') - 1;
                    i += 2;
                } else ans += 'a' + s[i] - '0' - 1;
            }
            return ans;
        }
    };
    
  • # 1309. Decrypt String from Alphabet to Integer Mapping
    # https://leetcode.com/problems/decrypt-string-from-alphabet-to-integer-mapping/
    
    class Solution:
        def freqAlphabets(self, s: str) -> str:
            res = []
            n = len(s)
            i = 0
            
            while i < n:
                
                if i + 2 < n and s[i+2] == "#" and 10 <= int(s[i:i+2]) <= 26:
                    res.append(chr(ord('a') + int(s[i:i+2]) - 1))
                    i += 3
                
                else:
                    res.append(chr(ord('a') + int(s[i]) - 1))
                    i += 1
            
            return "".join(res)
    

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