LeetCode: Max Number of K-Sum Pairs

Find the maximum number of k-sum pairs in an array.

See original problem on leetcode.com

Difficulty: Medium

Solution

I really 🩷 these two-pointer problems!

Start by sorting nums. Initialize count, left, and right.

If the sum of nums[left] and nums[right] is less than the target, then we need to make the smaller number bigger. Move left to the right.

If the sum of nums[left] and nums[right] is greater than the target, then we need to make the bigger number smaller. Move right to the left.

If the sum of nums[left] and nums[right] equals the target, increment count and move both pointers inward.

class Solution:
    def maxOperations(self, nums: List[int], k: int) -> int:
        nums.sort()
        count = 0
        left, right = 0, len(nums) - 1

        while left < right:
            if nums[left] + nums[right] < k:
                left += 1
            elif nums[left] + nums[right] > k:
                right -= 1
            else:
                count += 1
                left += 1
                right -= 1

        return count