Count symmetric integers

Math Enumeration

83.1% acceptance

Feb 25, 2026

647

You are given two positive integers low and high. An integer x consisting of 2 * n digits is symmetric if the sum of the first n digits of x is equal to the sum of the last n digits of x. Numbers with an odd number of digits are never symmetric. Return the number of symmetric integers in the range [low, high].

Solution

Rust

Time O(n)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn count_symmetric_integers(low: i32, high: i32) -> i32 {
    (low..=high).filter(|&n| {
      let s = n.to_string();
      let len = s.len();
      if len % 2 != 0 { return false; }
      let b = s.as_bytes();
      let half = len / 2;
      let left: i32 = b[..half].iter().map(|&c| (c - b'0') as i32).sum();
      let right: i32 = b[half..].iter().map(|&c| (c - b'0') as i32).sum();
      left == right
    }).count() as i32
  }
}