README_EN.md

17.10. Find Majority Element

中文文档

Description

A majority element is an element that makes up more than half of the items in an array. Given a positive integers array, find the majority element. If there is no majority element, return -1. Do this in O(N) time and O(1) space.

Example 1:

Input: [1,2,5,9,5,9,5,5,5]

Output: 5

 

Example 2:

Input: [3,2]

Output: -1

 

Example 3:

Input: [2,2,1,1,1,2,2]

Output: 2

Solutions

Boyer–Moore majority vote algorithm

Python3

class Solution:
    def majorityElement(self, nums: List[int]) -> int:
        cnt = major = 0
        for num in nums:
            if cnt == 0:
                major = num
                cnt = 1
            else:
                cnt += (1 if major == num else -1)
        return major

Java

class Solution {
    public int majorityElement(int[] nums) {
        int cnt = 0, major = 0;
        for (int num : nums) {
            if (cnt == 0) {
                major = num;
                cnt = 1;
            } else {
                cnt += (major == num ? 1 : -1);
            }
        }
        return major;
    }
}

JavaScript

/**
 * @param {number[]} nums
 * @return {number}
 */
var majorityElement = function(nums) {
    let cnt = 0;
    let major = 0;
    for (const num of nums) {
        if (cnt == 0) {
            major = num;
            cnt = 1;
        } else {
            cnt += (major == num ? 1 : -1);
        }
    }
    return major;
};

C++

class Solution {
public:
    int majorityElement(vector<int>& nums) {
        int cnt = 0, major = 0;
        for (int num : nums) {
            if (cnt == 0) {
                major = num;
                cnt = 1;
            } else {
                cnt += (major == num ? 1 : -1);
            }
        }
        return major;
    }
};

C#

public class Solution {
    public int MajorityElement(int[] nums) {
        int cnt = 0, major = 0;
        foreach (int num in nums)
        {
            if (cnt == 0)
            {
                major = num;
                cnt = 1;
            }
            else
            {
                cnt += (major == num ? 1 : -1);
            }
        }
        return major;
    }
}

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