Sum of digits of string after convert

String Simulation

74.8% acceptance

Feb 25, 2026

1198

104

You are given a string s consisting of lowercase English letters, and an integer k. Your task is to convert the string into an integer by a special process, and then transform it by summing its digits repeatedly k times. More specifically, perform the following steps: Convert s into an integer by replacing each letter with its position in the alphabet (i.e. replace 'a' with 1, 'b' with 2, ..., 'z' with 26). Transform the integer by replacing it with the sum of its digits. Repeat the transform operation (step 2) k times in total.

Solution

Rust

Time O(n²)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn get_lucky(s: String, k: i32) -> i32 {
    // Convert to digit string
    let mut num_str = String::new();
    for b in s.bytes() {
      num_str.push_str(&((b - b'a' + 1) as u32).to_string());
    }

    let mut val: i32 = num_str.bytes().map(|b| (b - b'0') as i32).sum();
    for _ in 1..k {
      let mut sum = 0;
      let mut v = val;
      while v > 0 {
        sum += v % 10;
        v /= 10;
      }
      val = sum;
    }
    val
  }
}