LeetCode 1309: Decrypt String from Alphabet to Integer Mapping Solution

Master LeetCode problem 1309 (Decrypt String from Alphabet to Integer Mapping), a easy challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

1309. Decrypt String from Alphabet to Integer Mapping

Easy

String

Problem Explanation

Explanation

To solve this problem, we can iterate through the given string s from right to left. If we encounter a #, we know the next two characters represent a letter. If not, the current character represents a letter. We can then map the corresponding letter and append it to our result string. We continue this process until we have processed all characters in s.

Time complexity: O(n), where n is the length of the input string s.
Space complexity: O(n) for storing the result string.

Solution Code

class Solution {
    public String freqAlphabets(String s) {
        StringBuilder result = new StringBuilder();
        int i = s.length() - 1;
        while (i >= 0) {
            if (s.charAt(i) == '#') {
                int num = Integer.parseInt(s.substring(i - 2, i));
                result.insert(0, (char) ('a' + num - 1));
                i -= 3;
            } else {
                result.insert(0, (char) ('a' + (s.charAt(i) - '0' - 1)));
                i--;
            }
        }
        return result.toString();
    }
}

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