Max Number of K-Sum Pairs — LeetCode 1679 Python Solution

The problem

You are given an integer array nums and an integer k. In one operation, you can pick two numbers from the array whose sum equals k and remove them from the array.

Example

Input

nums = [1,2,3,4], k = 5

Output

2

Explanation

Starting with nums = [1,2,3,4]:

Python solution

class Solution:
    def maxOperations(self, nums: List[int], k: int) -> int:
        nums.sort()
        l, r, ans = 0, len(nums) - 1, 0
        while l < r:
            s = nums[l] + nums[r]
            if s == k:
                ans += 1
                l, r = l + 1, r - 1
            elif s > k:
                r -= 1
            else:
                l += 1
        return ans

Complexity

Pattern: Two Pointers

Use the order already in the input to discard half the search space at every step. LeetCode 1679. Max Number of K-Sum Pairs is filed here because LeetCode tags it Two Pointers, which is the vocabulary this hub collects.

The two pointers guide has the Python template for the pattern and the 201 LeetCode problems that use it.

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