题目如下:
You are given an integer array
nums
and an integerk
.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
解题思路:首先统计出每个num出现的次数,然后求num和k-num出现次数的较小值,即为这对组合可操作的次数,注意要考虑 num = k- num的情况。
代码如下:
class Solution(object): def maxOperations(self, nums, k): """ :type nums: List[int] :type k: int :rtype: int """ dic = {} res = 0 for num in nums: dic[num] = dic.setdefault(num,0) + 1 for key in dic.iterkeys(): if dic[key] <= 0:continue elif k - key == key: res += dic[key]/2 dic[key] = dic[key] % 2 elif k - key in dic: pair = min(dic[key],dic[k-key]) res += pair dic[key] -= pair dic[k-key] -= pair return res