Decode the message

Hash Table String

85.8% acceptance

Feb 25, 2026

1128

113

You are given the strings key and message, which represent a cipher key and a secret message. Use the first appearance of all 26 lowercase English letters in key as the order of the substitution table. Align the substitution table with the regular English alphabet. Each letter in message is substituted using the table. Spaces are transformed to themselves. Return the decoded message.

Solution

Rust

Time O(n)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn decode_message(key: String, message: String) -> String {
    let mut table = [' '; 26];
    let mut idx = 0u8;
    for c in key.chars() {
      if c != ' ' {
        let i = (c as u8 - b'a') as usize;
        if table[i] == ' ' {
          table[i] = (b'a' + idx) as char;
          idx += 1;
        }
      }
    }
    message.chars().map(|c| {
      if c == ' ' { ' ' } else { table[(c as u8 - b'a') as usize] }
    }).collect()
  }
}