LC 3347. 执行操作后元素的最高频率 II

https://leetcode.cn/problems/maximum-frequency-of-an-element-after-performing-operations-ii/description/

这题的关键在于选出可能的特征值出来，大约有三种： a) nums b) nums + k c) nums - k.

选出来可能的特征值之后，使用双指针的办法去寻找这些特征值可能覆盖的范围就行。 

class Solution:
    def maxFrequency(self, nums: List[int], k: int, numOperations: int) -> int:
        from collections import Counter
        cnt = Counter(nums)
        tmp = sorted(nums)
        cand = sorted(set([x - k for x in nums] + [x + k for x in nums] + nums))
        # print(cand)
        n = len(nums)
        i, j = 0, 0
        ans = 0
        for c in cand:
            while i < n and tmp[i] + k < c:
                i += 1
            while j < n and tmp[j] - k <= c:
                j += 1
            sz = min(numOperations, j - i - cnt[c]) + cnt[c]
            # print(c, sz)
            ans = max(ans, sz)
        return ans