LeetCode 229. Majority Element II

Given an integer array of size n, find all elements that appear more than ⌊ n/3 ⌋ times. The algorithm should run in linear time and in O(1) space.

Extended version of http://blog.youkuaiyun.com/github_34333284/article/details/51118586

#include <iostream>
#include <vector>
#include <climits>
using namespace std;

vector<int> majorityElement(vector<int>& nums) {
    int count1 = 0;
    int count2 = 0;
    int target1 = INT_MIN;
    int target2 = INT_MIN;
    for(int i = 0; i < nums.size(); ++i) {
        if(nums[i] == target1) {
            count1++;
        } else if(nums[i] == target2) {   // the if-else if- else sequence matters!
             count2++;
        } else if(count1 == 0) {
            target1 = nums[i];
            count1++;
        } else if(count2 == 0) {
            target2 = nums[i];
            count2++;
        } else {
            count1--;
            count2--;
        }
    }
    vector<int> res;
    count1 = 0, count2 = 0;
    for(auto num : nums) {
        if(num == target1) count1++;
        else if(num == target2) count2++;
    }
    if(count1 > nums.size() / 3) res.push_back(target1);
    if(count2 > nums.size() / 3) res.push_back(target2);
    return res;
}

int main(void) {
    vector<int> nums{1, 2, 2, 3, 2, 1, 1, 3};
    vector<int> res = majorityElement(nums);
    cout << res[0] << endl;
    cout << res[1] << endl;
}