911. Online Election

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].

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预先生成好答案。调用q的时候用binary search。这里简单一点用treemap来作个弊
constructor O(n), q O(lg n)

class TopVotedCandidate {
    
    private TreeMap<Integer, Integer> winners;
    public TopVotedCandidate(int[] persons, int[] times) {
        winners = new TreeMap<>();
        Map<Integer, Integer> personToVotes = new HashMap<>();
        int winner = -1;
        personToVotes.put(winner, 0);
        
        for (int i = 0; i < persons.length; i++) {
            int p = persons[i];
            
            personToVotes.put(p, personToVotes.getOrDefault(p, 0) + 1);
            if (personToVotes.get(p) >= personToVotes.get(winner)) {                
                winner = p;
            }
            
            winners.put(times[i], winner);
        }
    }
    
    public int q(int t) {
        return winners.floorEntry(t).getValue();
    }
}

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