Question

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

Solution 1

class Solution:
  def majorityElement(self, nums: List[int]) -> int:
    cnt = m = 0
    for v in nums:
      if cnt == 0:
        m, cnt = v, 1
      else:
        cnt += 1 if m == v else -1
    return m if nums.count(m) > len(nums) // 2 else -1

class Solution {
  public int majorityElement(int[] nums) {
    int cnt = 0, m = 0;
    for (int v : nums) {
      if (cnt == 0) {
        m = v;
        cnt = 1;
      } else {
        cnt += (m == v ? 1 : -1);
      }
    }
    cnt = 0;
    for (int v : nums) {
      if (m == v) {
        ++cnt;
      }
    }
    return cnt > nums.length / 2 ? m : -1;
  }
}

class Solution {
public:
  int majorityElement(vector<int>& nums) {
    int cnt = 0, m = 0;
    for (int& v : nums) {
      if (cnt == 0) {
        m = v;
        cnt = 1;
      } else
        cnt += (m == v ? 1 : -1);
    }
    cnt = count(nums.begin(), nums.end(), m);
    return cnt > nums.size() / 2 ? m : -1;
  }
};

func majorityElement(nums []int) int {
  cnt, m := 0, 0
  for _, v := range nums {
    if cnt == 0 {
      m, cnt = v, 1
    } else {
      if m == v {
        cnt++
      } else {
        cnt--
      }
    }
  }
  cnt = 0
  for _, v := range nums {
    if m == v {
      cnt++
    }
  }
  if cnt > len(nums)/2 {
    return m
  }
  return -1
}

/**
 * @param {number[]} nums
 * @return {number}
 */
var majorityElement = function (nums) {
  let cnt = 0,
    m = 0;
  for (const v of nums) {
    if (cnt == 0) {
      m = v;
      cnt = 1;
    } else {
      cnt += m == v ? 1 : -1;
    }
  }
  cnt = 0;
  for (const v of nums) {
    if (m == v) {
      ++cnt;
    }
  }
  return cnt > nums.length / 2 ? m : -1;
};

public class Solution {
  public int MajorityElement(int[] nums) {
    int cnt = 0, m = 0;
    foreach (int v in nums)
    {
      if (cnt == 0)
      {
        m = v;
        cnt = 1;
      }
      else
      {
        cnt += m == v ? 1 : -1;
      }
    }
    cnt = 0;
    foreach (int v in nums)
    {
      if (m == v)
      {
        ++cnt;
      }
    }
    return cnt > nums.Length / 2 ? m : -1;
  }
}