# 12.02.2025 [2342. Max Sum of a Pair With Equal Sum of Digits]

Max pairs sum with equal digits sum #medium

12.02.2025

2342. Max Sum of a Pair With Equal Sum of Digits medium blog post substack youtube

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Problem TLDR

Max pairs sum with equal digits sum #medium

Intuition

Group numbers by digits sums, find two largest elements.

Approach

• the maximum key is 9 * 9 = 81

• shortest golf requires sorting, time degrades 300ms vs 14ms

Complexity

• Time complexity: $$O(n)$$, O(nlog(n)) for Kotlin golf

• Space complexity: $$O(1)$$, O(n) for golf

Code

    fun maximumSum(nums: IntArray) = nums
        .groupBy { "$it".sumOf { it - '0' } }.filter { it.value.size > 1 }
        .maxOfOrNull { it.value.sorted().takeLast(2).sum() } ?: -1

    pub fn maximum_sum(nums: Vec<i32>) -> i32 {
        let (mut s, mut r) = (vec![0; 99], -1);
        for x in nums {
            let (mut k, mut n) = (0, x as usize); 
            while n > 0 { k += n % 10; n /= 10 }
            if s[k] > 0 { r = r.max(s[k] + x) }; s[k] = s[k].max(x)
        }; r
    }

    int maximumSum(vector<int>& nums) {
        int s[99]{}, r = -1;
        for (int x: nums) {
            int k = 0, n = x; for (;n; n /= 10) k += n % 10;
            r = max(r, s[k] ? s[k] + x : r);
            s[k] = max(s[k], x);
        } return r;
    }