README.md

911. 在线选举

English Version

题目描述

给你两个整数数组 persons 和 times 。在选举中，第 i 张票是在时刻为 times[i] 时投给候选人 persons[i] 的。

对于发生在时刻 t 的每个查询，需要找出在 t 时刻在选举中领先的候选人的编号。

在 t 时刻投出的选票也将被计入我们的查询之中。在平局的情况下，最近获得投票的候选人将会获胜。

实现 TopVotedCandidate 类：

• TopVotedCandidate(int[] persons, int[] times) 使用 persons 和 times 数组初始化对象。
• int q(int t) 根据前面描述的规则，返回在时刻 t 在选举中领先的候选人的编号。

 

示例：

输入：
["TopVotedCandidate", "q", "q", "q", "q", "q", "q"]
[[[0, 1, 1, 0, 0, 1, 0], [0, 5, 10, 15, 20, 25, 30]], [3], [12], [25], [15], [24], [8]]
输出：
[null, 0, 1, 1, 0, 0, 1]

解释：
TopVotedCandidate topVotedCandidate = new TopVotedCandidate([0, 1, 1, 0, 0, 1, 0], [0, 5, 10, 15, 20, 25, 30]);
topVotedCandidate.q(3); // 返回 0 ，在时刻 3 ，票数分布为 [0] ，编号为 0 的候选人领先。
topVotedCandidate.q(12); // 返回 1 ，在时刻 12 ，票数分布为 [0,1,1] ，编号为 1 的候选人领先。
topVotedCandidate.q(25); // 返回 1 ，在时刻 25 ，票数分布为 [0,1,1,0,0,1] ，编号为 1 的候选人领先。（在平局的情况下，1 是最近获得投票的候选人）。
topVotedCandidate.q(15); // 返回 0
topVotedCandidate.q(24); // 返回 0
topVotedCandidate.q(8); // 返回 1

 

提示：

• 1 <= persons.length <= 5000
• times.length == persons.length
• 0 <= persons[i] < persons.length
• 0 <= times[i] <= 109
• times 是一个严格递增的有序数组
• times[0] <= t <= 109
• 每个测试用例最多调用 104 次 q

解法

二分查找。

先预处理得到每个时刻的领先的候选人编号 wins[i]。

然后对于每次查询 q，二分查找得到小于等于 t 时刻的最大时刻 left，返回 wins[left] 即可。

Python3

class TopVotedCandidate:
    def __init__(self, persons: List[int], times: List[int]):
        mx = cur = 0
        counter = Counter()
        self.times = times
        self.wins = []
        for i, p in enumerate(persons):
            counter[p] += 1
            if counter[p] >= mx:
                mx, cur = counter[p], p
            self.wins.append(cur)

    def q(self, t: int) -> int:
        left, right = 0, len(self.wins) - 1
        while left < right:
            mid = (left + right + 1) >> 1
            if self.times[mid] <= t:
                left = mid
            else:
                right = mid - 1
        return self.wins[left]


# Your TopVotedCandidate object will be instantiated and called as such:
# obj = TopVotedCandidate(persons, times)
# param_1 = obj.q(t)

Java

class TopVotedCandidate {
    private int[] times;
    private int[] winPersons;

    public TopVotedCandidate(int[] persons, int[] times) {
        this.times = times;
        int mx = -1, curWin = -1;
        int n = persons.length;
        int[] counter = new int[n + 1];
        winPersons = new int[n];
        for (int i = 0; i < n; ++i) {
            if (++counter[persons[i]] >= mx) {
                mx = counter[persons[i]];
                curWin = persons[i];
            }
            winPersons[i] = curWin;
        }
    }

    public int q(int t) {
        int left = 0, right = winPersons.length - 1;
        while (left < right) {
            int mid = (left + right + 1) >> 1;
            if (times[mid] <= t) {
                left = mid;
            } else {
                right = mid - 1;
            }
        }
        return winPersons[left];
    }
}

/**
 * Your TopVotedCandidate object will be instantiated and called as such:
 * TopVotedCandidate obj = new TopVotedCandidate(persons, times);
 * int param_1 = obj.q(t);
 */

C++

class TopVotedCandidate {
public:
    vector<int> times;
    vector<int> wins;

    TopVotedCandidate(vector<int>& persons, vector<int>& times) {
        int n = persons.size();
        wins.resize(n);
        int mx = 0, cur = 0;
        this->times = times;
        vector<int> counter(n);
        for (int i = 0; i < n; ++i) {
            int p = persons[i];
            if (++counter[p] >= mx) {
                mx = counter[p];
                cur = p;
            }
            wins[i] = cur;
        }
    }

    int q(int t) {
        int left = 0, right = wins.size() - 1;
        while (left < right) {
            int mid = left + right + 1 >> 1;
            if (times[mid] <= t)
                left = mid;
            else
                right = mid - 1;
        }
        return wins[left];
    }
};

/**
 * Your TopVotedCandidate object will be instantiated and called as such:
 * TopVotedCandidate* obj = new TopVotedCandidate(persons, times);
 * int param_1 = obj->q(t);
 */

Go

type TopVotedCandidate struct {
	times []int
	wins  []int
}

func Constructor(persons []int, times []int) TopVotedCandidate {
	mx, cur, n := 0, 0, len(persons)
	counter := make([]int, n)
	wins := make([]int, n)
	for i, p := range persons {
		counter[p]++
		if counter[p] >= mx {
			mx = counter[p]
			cur = p
		}
		wins[i] = cur
	}
	return TopVotedCandidate{times, wins}
}

func (this *TopVotedCandidate) Q(t int) int {
	left, right := 0, len(this.wins)-1
	for left < right {
		mid := (left + right + 1) >> 1
		if this.times[mid] <= t {
			left = mid
		} else {
			right = mid - 1
		}
	}
	return this.wins[left]
}

/**
 * Your TopVotedCandidate object will be instantiated and called as such:
 * obj := Constructor(persons, times);
 * param_1 := obj.Q(t);
 */

...