Leetcode 2815. Max Pair Sum in an Array

Accepted solution but not optimized.

You are given a 0-indexed integer array nums. You have to find the maximum sum of a pair of numbers from nums such that the maximum digit in both numbers are equal.

Return the maximum sum or -1 if no such pair exists.

Example 1:

Input: nums = [51,71,17,24,42]
Output: 88
Explanation:
For i = 1 and j = 2, nums[i] and nums[j] have equal maximum digits with a pair sum of 71 + 17 = 88.
For i = 3 and j = 4, nums[i] and nums[j] have equal maximum digits with a pair sum of 24 + 42 = 66.
It can be shown that there are no other pairs with equal maximum digits, so the answer is 88.

Example 2:

Input: nums = [1,2,3,4]
Output: -1
Explanation: No pair exists in nums with equal maximum digits.

class Solution {
public:
    int maxSum(vector<int>& nums) {
        int maxAnswer = -1;
        vector<int>largestDigit ={};
        int numsSize = nums.size();
        for(int i=0; i < numsSize; i++){
            largestDigit.push_back(maxInt(nums[i]));
        }
        
        for(int i=0; i < numsSize; i++){
            for(int j=i+1; j < numsSize; j++){
                if(largestDigit[i] == largestDigit[j])
                {
                     maxAnswer = max(maxAnswer, nums[i] + nums[j]);
                }
            }
        }
        return maxAnswer;
    }
    
    int maxInt(int n)
    {
        int maxInteger = 0;
        while(n > 0){
        maxInteger = max(maxInteger, n%10);
            n = n/10;
            //372/10 = 37---devide (2)---mode
        }
        return maxInteger;
    }
};

Optimized version as per Vlad https://leetcode.com/votrubac/

class Solution {
public:
    int maxSum(vector<int>& nums) {
        int maxAnswer = -1;
        int digitArr[10] = {};
        int numsSize = nums.size();
        for(int i=0; i < numsSize; i++){
            int maxDigit = getMaxDigit(nums[i]);
            //if digit array already has the value for a given digit
            if(digitArr[maxDigit])
            {
                maxAnswer = max(maxAnswer, digitArr[maxDigit] + nums[i]);
            }
            digitArr[maxDigit] = max(digitArr[maxDigit], nums[i]); 
        }        
        return maxAnswer;
    }
    
    int getMaxDigit(int n)
    {
        int maxDigitValue = 0;
        while(n > 0){
        maxDigitValue = max(maxDigitValue, n%10);
            n = n/10;
            //372/10 = 37---devide (2)---mode
        }
        return maxDigitValue;
    }
};