LeetCode - Majority Element

問題の説明

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.

I/O例

Example 1:

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

Example 2:

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

せいげんじょうけん

Constraints:

n == nums.length
1 <= n <= 5 * 104
-231 <= nums[i] <= 231 - 1

Solution

ソート後、maxCountの要素を順番にナビゲートして検索します.
[方法2]ハッシュマッピングを使用して各要素のカウントを計算する
[方法3]Boyer-Moore Vootingアルゴリズム(ソリューションを参照)
-多くの要素が配列全体の2/n以上を占めます.

class Solution {
    public int majorityElement(int[] nums) {
        int count = 0;
        int candidate = 0;

        for (int num : nums) {
            if (count == 0) {
                candidate = num;
            }
            count += (num == candidate) ? 1 : -1;
        }

        return candidate;
    }
}