169. Majority Element

Given an array nums of size n, return the majority element.

The majority element is the element that appears more than ⌊n / 2⌋ times. You may assume that the majority element always exists in the array.

Example 1:

Input: nums = [3,2,3]
Output: 3

Example 2:

Input: nums = [2,2,1,1,1,2,2]
Output: 2

Constraints:

• n == nums.length
• 1 <= n <= 5 * 104
• -10^9 <= nums[i] <= 10^9

Follow-up:

Could you solve the problem in linear time and in O(1) space?

Code

C++ using sort

class Solution {
public:
    int majorityElement(vector<int>& nums) {
    
        sort(nums.begin(), nums.end());
        int n = nums.size();
        return nums[n/2];
    }
};

C++ using Moore Voting

class Solution {
public:

    // Moore voting
    int majorityElement2(vector<int>& nums) {
    
        int count = 0;
        int major = 0;

        for (int num : nums) {
            if (count == 0) 
            	major = num;
            if (major == num) 
            	count++;
			else count--;
        }
    	return major;
    }
};