Majority_Element_2.cpp

#include <bits/stdc++.h>

vector<int> majorityElementII(vector<int> &v)
{
    // Write your code here.
    int n = v.size(); // size of the array

    int cnt1 = 0, cnt2 = 0; // counts
    int el1 = INT_MIN;      // element 1
    int el2 = INT_MIN;      // element 2

    // applying the Extended Boyer Moore's Voting Algorithm:
    for (int i = 0; i < n; i++)
    {
        if (cnt1 == 0 && el2 != v[i])
        {
            cnt1 = 1;
            el1 = v[i];
        }
        else if (cnt2 == 0 && el1 != v[i])
        {
            cnt2 = 1;
            el2 = v[i];
        }
        else if (v[i] == el1)
            cnt1++;
        else if (v[i] == el2)
            cnt2++;
        else
        {
            cnt1--, cnt2--;
        }
    }

    vector<int> ls; // list of answers

    // Manually check if the stored elements in
    // el1 and el2 are the majority elements:
    cnt1 = 0, cnt2 = 0;
    for (int i = 0; i < n; i++)
    {
        if (v[i] == el1)
            cnt1++;
        if (v[i] == el2)
            cnt2++;
    }

    int mini = int(n / 3) + 1;
    if (cnt1 >= mini)
        ls.push_back(el1);
    if (cnt2 >= mini)
        ls.push_back(el2);

    // Uncomment the following line
    // if it is told to sort the answer array:
    // sort(ls.begin(), ls.end()); //TC --> O(2*log2) ~ O(1);

    return ls;
}