Max sum of a pair with equal sum of digits

Array Hash Table Sorting Heap (Priority Queue)

66.0% acceptance

Feb 25, 2026

1405

You are given a 0-indexed array nums consisting of positive integers. You can choose two indices i and j, such that i != j, and the sum of digits of the number nums[i] is equal to that of nums[j]. Return the maximum value of nums[i] + nums[j] that you can obtain over all possible indices i and j that satisfy the conditions. If no such pair of indices exists, return -1.

Solution

Rust

Time O(n)

Space O(n)

LeetCode

solution.rs

use std::collections::HashMap;


impl Solution {
  pub fn maximum_sum(nums: Vec<i32>) -> i32 {
    let digit_sum = |mut n: i32| -> i32 {
      let mut s = 0;
      while n > 0 { s += n % 10; n /= 10; }
      s
    };
    let mut best: HashMap<i32, i32> = HashMap::new();
    let mut ans = -1i32;
    for n in nums {
      let s = digit_sum(n);
      if let Some(&prev) = best.get(&s) {
        ans = ans.max(prev + n);
        best.insert(s, prev.max(n));
      } else {
        best.insert(s, n);
      }
    }
    ans
  }
}