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中等
设计
数组
哈希表
二分查找

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

方法一：二分查找

我们可以在初始化时，记录每个时刻的胜者，然后在查询时，使用二分查找找到小于等于 $t$ 的最大时刻，返回该时刻的胜者。

初始化时，我们使用一个计数器 $cnt$ 记录每个候选人的票数，用一个变量 $cur$ 记录当前领先的候选人。然后遍历每个时刻，更新 $cnt$ 和 $cur$，并记录每个时刻的胜者。

查询时，我们使用二分查找找到小于等于 $t$ 的最大时刻，返回该时刻的胜者。

时间复杂度方面，初始化时，我们需要 $O(n)$ 的时间，查询时，我们需要 $O(\log n)$ 的时间。空间复杂度为 $O(n)$。

Python3

class TopVotedCandidate:

    def __init__(self, persons: List[int], times: List[int]):
        cnt = Counter()
        self.times = times
        self.wins = []
        cur = 0
        for p in persons:
            cnt[p] += 1
            if cnt[cur] <= cnt[p]:
                cur = p
            self.wins.append(cur)

    def q(self, t: int) -> int:
        i = bisect_right(self.times, t) - 1
        return self.wins[i]


# 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[] wins;

    public TopVotedCandidate(int[] persons, int[] times) {
        int n = persons.length;
        wins = new int[n];
        this.times = times;
        int[] cnt = new int[n];
        int cur = 0;
        for (int i = 0; i < n; ++i) {
            int p = persons[i];
            ++cnt[p];
            if (cnt[cur] <= cnt[p]) {
                cur = p;
            }
            wins[i] = cur;
        }
    }

    public int q(int t) {
        int i = Arrays.binarySearch(times, t + 1);
        i = i < 0 ? -i - 2 : i - 1;
        return wins[i];
    }
}

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

    int q(int t) {
        int i = upper_bound(times.begin(), times.end(), t) - times.begin() - 1;
        return wins[i];
    }

private:
    vector<int> times;
    vector<int> wins;
};

/**
 * 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 {
	n := len(persons)
	wins := make([]int, n)
	cnt := make([]int, n)
	cur := 0
	for i, p := range persons {
		cnt[p]++
		if cnt[cur] <= cnt[p] {
			cur = p
		}
		wins[i] = cur
	}
	return TopVotedCandidate{times, wins}
}

func (this *TopVotedCandidate) Q(t int) int {
	i := sort.SearchInts(this.times, t+1) - 1
	return this.wins[i]
}

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

TypeScript

class TopVotedCandidate {
    private times: number[];
    private wins: number[];

    constructor(persons: number[], times: number[]) {
        const n = persons.length;
        this.times = times;
        this.wins = new Array<number>(n).fill(0);
        const cnt: Array<number> = new Array<number>(n).fill(0);
        let cur = 0;
        for (let i = 0; i < n; ++i) {
            const p = persons[i];
            cnt[p]++;
            if (cnt[cur] <= cnt[p]) {
                cur = p;
            }
            this.wins[i] = cur;
        }
    }

    q(t: number): number {
        const search = (t: number): number => {
            let l = 0,
                r = this.times.length;
            while (l < r) {
                const mid = (l + r) >> 1;
                if (this.times[mid] > t) {
                    r = mid;
                } else {
                    l = mid + 1;
                }
            }
            return l;
        };
        const i = search(t) - 1;
        return this.wins[i];
    }
}

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