[Leetcode 229, Medium] Majority Element II

Problem:

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.

Analysis:

Use Boyer-Moore voting algorithm (https://en.wikipedia.org/wiki/Boyer%E2%80%93Moore_majority_vote_algorithm ) , and then test the candidate elements are eligible for majority elements.

Solutions:

C++:

    vector<int> majorityElement(vector<int>& nums) {
        vector<int> results;
        if(nums.empty())
            return results;
            
        if(nums.size() == 1) {
            results.push_back(nums[0]);
            return results;
        }

        int first = 0, second = 0, f_count = 0, s_count = 0;
        for(int i = 0; i < nums.size(); ++i) {
            if(f_count == 0) {
                first = nums[i];
                ++f_count;
            } else if(nums[i] == first) {
                ++f_count;
            }else if(s_count == 0) {
                second = nums[i];
                ++s_count;
            } else if(nums[i] == second) {
                ++s_count;
            } else {
                --f_count;
                --s_count;
            }
        }
        
        f_count = 0;
        s_count = 0;
        for(int i = 0; i < nums.size(); ++i) {
            if(nums[i] == first)
                ++f_count;
            else if(nums[i] == second)
                ++s_count;
        }
        
        if(f_count > nums.size() / 3)
            results.push_back(first);
            
        if(s_count > nums.size() / 3)
            results.push_back(second);
    }

Java:

Python: