1679 Max Number of K-Sum Pairs.py

# 1679. Max Number of K-Sum Pairs

# 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.
# Return the maximum number of operations you can perform on the array.

# Example 1:

# Input: nums = [1,2,3,4], k = 5
# Output: 2
# Explanation: Starting with nums = [1,2,3,4]:
# - Remove numbers 1 and 4, then nums = [2,3]
# - Remove numbers 2 and 3, then nums = []
# There are no more pairs that sum up to 5, hence a total of 2 operations.
# Example 2:

# Input: nums = [3,1,3,4,3], k = 6
# Output: 1
# Explanation: Starting with nums = [3,1,3,4,3]:
# - Remove the first two 3's, then nums = [1,4,3]
# There are no more pairs that sum up to 6, hence a total of 1 operation.

# Constraints:

# 1 <= nums.length <= 105
# 1 <= nums[i] <= 109
# 1 <= k <= 109

class Solution:
    def maxOperations(self, nums: [int], k: int) -> int:
        # sorting allows us to narrow down the search space
        nums.sort()
        
        count = 0
        i = 0
        j = len(nums) - 1

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

        return count