【朱迪的LeetCode刷题笔记】】1679. Max Number of K-Sum Pairs #Easy #Python

Judie

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

Judy
Python hash table

class Solution(object):
    def maxOperations(self, nums, k):
        """
        :type nums: List[int]
        :type k: int
        :rtype: int
        """
        d = {}
        c = 0
        for i, x in enumerate(nums):
            if x in d and d[x] > 0:
                c += 1
                d[x] -= 1
            elif k-x in d:
                d[k-x] += 1
            else:
                d[k-x] = 1
        return c

Sol1
Python slower? but oneliner! lol
https://leetcode.com/problems/ma ... p;envId=leetcode-75

class Solution:
    def maxOperations(self, nums, k):
        cnt, ans = Counter(nums), 0
        for val in cnt:
            ans += min(cnt[val], cnt[k - val])
        return ans//2

return (lambda c: sum(min(c[n], c[k-n]) for n in c))(Counter(nums))//2