Decrypt string from alphabet to integer mapping

String

80.5% acceptance

Feb 25, 2026

1606

120

You are given a string s formed by digits 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. The test cases are generated so that a unique mapping will always exist.

Solution

Rust

Time O(n)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn freq_alphabets(s: String) -> String {
    let bytes = s.as_bytes();
    let n = bytes.len();
    let mut res = String::new();
    let mut i = 0;
    while i < n {
      if i + 2 < n && bytes[i + 2] == b'#' {
        let num = (bytes[i] - b'0') as usize * 10 + (bytes[i + 1] - b'0') as usize;
        res.push((b'a' + (num - 1) as u8) as char);
        i += 3;
      } else {
        let num = (bytes[i] - b'0') as usize;
        res.push((b'a' + (num - 1) as u8) as char);
        i += 1;
      }
    }
    res
  }
}