Maximum 69 number

Math Greedy

84.5% acceptance

Feb 25, 2026

3307

240

You are given a positive integer num consisting only of digits 6 and 9. Return the maximum number you can get by changing at most one digit (6 becomes 9, and 9 becomes 6).

Solution

Rust

Time O(n)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn maximum69_number(num: i32) -> i32 {
    let s = num.to_string();
    if let Some(pos) = s.find('6') {
      let mut v: Vec<char> = s.chars().collect();
      v[pos] = '9';
      v.iter().collect::<String>().parse().unwrap()
    } else {
      num
    }
  }
}