Closest fair integer

Math Enumeration

44.3% acceptance

Mar 31, 2026

You are given a positive integer n. We call an integer k fair if the number of even digits in k is equal to the number of odd digits in it. Return the smallest fair integer that is greater than or equal to n.

Solution

Rust

Time O(n²)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn closest_fair(n: i32) -> i32 {
    let mut x = n;
    loop {
      let mut odd = 0;
      let mut even = 0;
      let mut tmp = x;
      while tmp > 0 {
        if (tmp % 10) % 2 == 0 { even += 1; } else { odd += 1; }
        tmp /= 10;
      }
      if odd == even { return x; }
      // If digit count is odd, skip to next even-digit number
      let digits = (odd + even) as u32;
      if digits % 2 == 1 {
        // smallest (digits+1)-digit number with equal odd/even
        // digits+1 is even. Half odd, half even. "10...0" with (digits+1) digits
        x = 10_i32.pow(digits);
        continue;
      }
      x += 1;
    }
  }
}