Maximum swap

Math Greedy

51.9% acceptance

Feb 20, 2026

4280

274

You are given an integer num. You can swap two digits at most once to get the maximum valued number. Return the maximum valued number you can get.

Solution

Rust

Time O(n²)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn maximum_swap(num: i32) -> i32 {
    let mut digits: Vec<u8> = num.to_string().bytes().map(|b| b - b'0').collect();
    let n = digits.len();
    // last[d] = last index of digit d
    let mut last = [0usize; 10];
    for i in 0..n {
      last[digits[i] as usize] = i;
    }
    for i in 0..n {
      for d in (digits[i] as usize + 1..=9).rev() {
        if last[d] > i {
          digits.swap(i, last[d]);
          return digits.iter().fold(0i32, |acc, &x| acc * 10 + x as i32);
        }
      }
    }
    num
  }
}