Max pair sum in an array

Array Hash Table

60.4% acceptance

Feb 25, 2026

436

137

You are given an integer array nums. You have to find the maximum sum of a pair of numbers from nums such that the largest digit in both numbers is equal. For example, 2373 is made up of three distinct digits: 2, 3, and 7, where 7 is the largest among them. Return the maximum sum or -1 if no such pair exists.

Solution

Rust

Time O(n)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn max_sum(nums: Vec<i32>) -> i32 {
    let max_digit = |mut n: i32| -> i32 { let mut mx = 0; while n > 0 { mx = mx.max(n % 10); n /= 10; } mx };
    let mut groups = [0i32; 10];
    let mut ans = -1i32;
    for &n in &nums {
      let key = max_digit(n) as usize;
      if groups[key] > 0 { ans = ans.max(groups[key] + n); }
      if n > groups[key] { groups[key] = n; }
    }
    ans
  }
}