[LeetCode]169.Majority Element，majorityelement

[LeetCode]169.Majority Element，majorityelement
【題目】

Given an array of size n, find the majority element. The majority element is the element that appears more than ⌊ n/2 ⌋ times.

You may assume that the array is non-empty and the majority element always exist in the array.

【分析】

思路是計算數組前一半出現元素的頻率，如果數目大於⌊ n/2 ⌋就返回

【代碼】

/**********************************   日期：2015-01-30*   作者：SJF0115*   題目: 169.Majority Element*   網址：https://oj.leetcode.com/problems/majority-element/*   結果：AC*   來源：LeetCode*   部落格：**********************************/#include <iostream>#include <vector>using namespace std;class Solution {public:    int majorityElement(vector<int> &num){        int len = num.size();        int size = len / 2 + 1;        int count;        // 統計前一半的元素個數        for(int i = 0;i < size;++i){            // 跳過重複元素            while(i > 0 && num[i] == num[i-1]){                ++i;            }//while            count = 0;            for(int j = i;j < len;++j){                if(num[j] == num[i]){                    ++count;                    if(count >= (len+1)/2){                        return num[i];                    }//if                }//if            }//for        }//for    }};int main(){    Solution solution;    vector<int> num = {8,8,7,7,7};    int result = solution.majorityElement(num);    // 輸出    cout<<result<<endl;    return 0;}

【分析二】

Every number in the vector votes for itself, the majority number gets the most votes. Different number offsets the votes.

遇到不同的就相互抵銷，遇到相同的就增加，當count = 0時，重新開始

【代碼二】

class Solution {public:    int majorityElement(vector<int> &num){        int vote = num[0];        int count = 1;        int size = num.size();        //vote from the second number        for(int i = 1;i < size;++i){            if(count == 0){                vote = num[i];                count++;            }//if            else if(vote == num[i]){                count++;            }            else{                count--;            }        }//for        return vote;    }};

【分析】

Majority Element肯定佔據至少一半的元素，因此排序後中間元素一定是Majority Element

【代碼】

class Solution {public:    int majorityElement(vector<int> &num){        int size = num.size();        // 只有一個元素        if(size == 1){            return num[0];        }//if        sort(num.begin(),num.end());        return num[size / 2];    }};