911. 在线选举

题目链接	911. 在线选举
思路	二分
题解链接	[Python/Java/JavaScript/Go] 二分查找
关键点	理解题意：预处理 - 按照times得出每个离散时刻下获胜者的person；询问 - 二分查找到>t的前一个时刻获胜者
时间复杂度	\(O(n)\)
空间复杂度	\(O(n)\)

代码实现：

class TopVotedCandidate:

    def __init__(self, persons: List[int], times: List[int]):
        n = len(times)
        self.times = times
        self.answer = [-1] * n

        cnts = defaultdict(int)
        winner = None
        for i, person in enumerate(persons):
            cnts[person] += 1
            if winner is None or cnts[person] >= cnts[winner]:
                winner = person
            self.answer[i] = winner
        self.n = n
            
    def q(self, t: int) -> int:
        left, right = -1, self.n
        while left + 1 < right:
            mid = (left+right) // 2
            if self.times[mid] <= t:
                left = mid
            else:
                right = mid
        return self.answer[right - 1]

Python-标准库

class TopVotedCandidate:

    def __init__(self, persons: List[int], times: List[int]):
        n = len(times)
        self.times = times
        self.answer = [-1] * n

        cnts = defaultdict(int)
        winner = None
        for i, person in enumerate(persons):
            cnts[person] += 1
            if winner is None or cnts[person] >= cnts[winner]:
                winner = person
            self.answer[i] = winner
            
    def q(self, t: int) -> int:
        return self.answer[
            bisect_right(self.times, t) - 1
        ]