947. Online Election¶

Difficulty: Medium

947. Online Election

Medium

You are given two integer arrays persons and times. In an election, the i^th vote was cast for persons[i] at time times[i].

For each query at a time t, find 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.

Implement the TopVotedCandidate class:

TopVotedCandidate(int[] persons, int[] times) Initializes the object with the persons and times arrays.
int q(int t) Returns the number of the person that was leading the election at time t according to the mentioned rules.

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
TopVotedCandidate topVotedCandidate = new TopVotedCandidate([0, 1, 1, 0, 0, 1, 0], [0, 5, 10, 15, 20, 25, 30]);
topVotedCandidate.q(3); // return 0, At time 3, the votes are [0], and 0 is leading.
topVotedCandidate.q(12); // return 1, At time 12, the votes are [0,1,1], and 1 is leading.
topVotedCandidate.q(25); // return 1, At time 25, the votes are [0,1,1,0,0,1], and 1 is leading (as ties go to the most recent vote.)
topVotedCandidate.q(15); // return 0
topVotedCandidate.q(24); // return 0
topVotedCandidate.q(8); // return 1

Constraints:

1 <= persons.length <= 5000
times.length == persons.length
0 <= persons[i] < persons.length
0 <= times[i] <= 10⁹
times is sorted in a strictly increasing order.
times[0] <= t <= 10⁹
At most 10⁴ calls will be made to q.

Solution¶

class TopVotedCandidate {
    private TreeSet<Integer> time;
    private HashMap<Integer, Integer> winnerId;
    private HashMap<Integer, Integer> votes;
    private TreeSet<Tuple> set;
    private HashMap<Tuple, Integer> timeMap;
    private int timer;

    static class Tuple {
        int pId, vFreq, vTime;
        public Tuple(int pId, int vFreq, int vTime) {
            this.pId = pId;
            this.vFreq = vFreq;
            this.vTime = vTime;
        }
        @Override
        public String toString() {
            return "(" + pId + " " + vFreq + " " + vTime + ")";
        }
        @Override
        public boolean equals(Object obj) {
            if (this == obj)
                return true;
            if (obj == null || getClass() != obj.getClass())
                return false;
            Tuple current = (Tuple)(obj);
            return current.pId == pId && current.vFreq == vFreq && current.vTime == vTime;
        }
        @Override
        public int hashCode() {
            return Objects.hash(pId, vFreq);
        }
    }

    static class customSort implements Comparator<Tuple> {
        @Override
        public int compare(Tuple first, Tuple second) {
            int op1 = Integer.compare(second.vFreq, first.vFreq);
            if (op1 != 0)
                return op1;
            return Integer.compare(second.vTime, first.vTime); 
        }
    }

    public TopVotedCandidate(int[] persons, int[] times) {
        time = new TreeSet<>();
        timeMap = new HashMap<>();
        winnerId = new HashMap<>();
        set = new TreeSet<>(new customSort());
        votes = new HashMap<>();
        timer = 0;

        for (int i = 0; i < persons.length; i++) {
            int currTime = times[i];
            int currVote = persons[i]; 
            if (votes.containsKey(currVote)) {
                int prevVotes = votes.get(currVote);
                set.remove(new Tuple(currVote, votes.get(currVote), timeMap.get(new Tuple(currVote, votes.get(currVote), -1))));
                set.add(new Tuple(currVote, votes.get(currVote) + 1, timer));
                votes.put(currVote, votes.get(currVote) + 1);
                timeMap.put(new Tuple(currVote, votes.get(currVote), -1), timer);
                timer++;
            } else {
                set.add(new Tuple(currVote, 1, timer));
                votes.put(currVote, 1);
                timeMap.put(new Tuple(currVote, 1, -1), timer);
                timer++;
            }
            winnerId.put(currTime, set.first().pId);
            time.add(currTime);
        } 
    }

    public int q(int t) {
        Integer prev = time.floor(t);
        return winnerId.get(prev); 
    }
}

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

Complexity Analysis¶

Time Complexity: O(?)
Space Complexity: O(?)

Approach¶

Detailed explanation of the approach will be added here