2815. Max Pair Sum in an Array
Description
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.
Constraints:
2 <= nums.length <= 100
1 <= nums[i] <= 104
Solutions
Solution 1: Enumeration
First, we initialize the answer variable $ans=-1$. Next, we directly enumerate all pairs $(nums[i], nums[j])$ where $i \lt j$, and calculate their sum $v=nums[i] + nums[j]$. If $v$ is greater than $ans$ and the largest digit of $nums[i]$ and $nums[j]$ are the same, then we update $ans$ with $v$.
The time complexity is $O(n^2 \times \log M)$, where $n$ is the length of the array and $M$ is the maximum value in the array.
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