911. Online Election

In an election, the i-th vote was cast for persons[i] at time times[i].

Now, we would like to implement the following query function: TopVotedCandidate.q(int t) will return the number of the person that was leading the election at time t.  

Votes cast at time t will count towards our query.  In the case of a tie, the most recent vote (among tied candidates) wins.

 

Example 1:

Input: ["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]]
Output: [null,0,1,1,0,0,1]
Explanation: 
At time 3, the votes are [0], and 0 is leading.
At time 12, the votes are [0,1,1], and 1 is leading.
At time 25, the votes are [0,1,1,0,0,1], and 1 is leading (as ties go to the most recent vote.)
This continues for 3 more queries at time 15, 24, and 8.

 

Note:

  1. 1 <= persons.length = times.length <= 5000
  2. 0 <= persons[i] <= persons.length
  3. times is a strictly increasing array with all elements in [0, 10^9].
  4. TopVotedCandidate.q is called at most 10000 times per test case.
  5. TopVotedCandidate.q(int t) is always called with t >= times[0].

Rust Solution

use std::collections::HashMap;

struct TopVotedCandidate {
    times: Vec<i32>,
    leaders: Vec<i32>,
}

impl TopVotedCandidate {
    fn new(persons: Vec<i32>, times: Vec<i32>) -> Self {
        let n = persons.len();
        let mut hm: HashMap<i32, usize> = HashMap::new();
        let mut leader: (usize, i32) = (0, 0);
        let mut leaders = vec![];
        for i in 0..n {
            let count = hm.entry(persons[i]).or_default();
            *count += 1;
            if *count >= leader.0 {
                leader = (*count, persons[i]);
            }
            leaders.push(leader.1);
        }
        TopVotedCandidate { times, leaders }
    }

    fn q(&self, t: i32) -> i32 {
        let i = match self.times.binary_search(&t) {
            Ok(i) => i,
            Err(i) => i - 1,
        };
        self.leaders[i]
    }
}

#[test]
fn test() {
    let persons = vec![0, 1, 1, 0, 0, 1, 0];
    let times = vec![0, 5, 10, 15, 20, 25, 30];
    let tvc = TopVotedCandidate::new(persons, times);
    assert_eq!(tvc.q(3), 0);
    assert_eq!(tvc.q(12), 1);
    assert_eq!(tvc.q(25), 1);
    assert_eq!(tvc.q(15), 0);
    assert_eq!(tvc.q(24), 0);
    assert_eq!(tvc.q(8), 1);
}

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