Minimum absolute distance between mirror pairs

Array Hash Table Math

44.3% acceptance

Feb 25, 2026

You are given an integer array nums. A mirror pair is a pair of indices (i, j) such that: 0 <= i < j < nums.length, and reverse(nums[i]) == nums[j], where reverse(x) denotes the integer formed by reversing the digits of x. Leading zeros are omitted after reversing, for example reverse(120) = 21. Return the minimum absolute distance between the indices of any mirror pair. The absolute distance between indices i and j is abs(i - j). If no mirror pair exists, return -1.

Solution

Rust

Time O(2^n)

Space O(n)

LeetCode

solution.rs

impl Solution {
  pub fn min_mirror_pair_distance(nums: Vec<i32>) -> i32 {
    fn reverse_num(mut n: i32) -> i32 {
      let mut r = 0i32;
      while n > 0 { r = r * 10 + n % 10; n /= 10; }
      r
    }
    use std::collections::HashMap;
    // For pair (i,j) with i<j: reverse(nums[i]) == nums[j]
    // For each i, store reverse(nums[i]) -> latest index i
    // Then for index j, look up nums[j] in map to find latest i < j with reverse(nums[i])==nums[j]
    let mut rev_map: HashMap<i32, usize> = HashMap::new();
    let mut ans = i32::MAX;
    for (j, &v) in nums.iter().enumerate() {
      if let Some(&i) = rev_map.get(&v) {
        ans = ans.min((j - i) as i32);
      }
      rev_map.insert(reverse_num(v), j);
    }
    if ans == i32::MAX { -1 } else { ans }
  }
}