Majority Element

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.

題目大意：

找出數組中超過一半的數。

 

C++實現代碼：

#include<iostream>
#include<vector>
using namespace std;

class Solution {
public:
    int majorityElement(vector<int> &num) {
        if(num.empty())
            return -1;
        int n=num.size();
        int i;
        int index=0;
        int count=1;
        for(i=1;i<n;i++)
        {
            if(num[i]==num[index])
            {
                count++;
            }
            else
                count--;
            if(count<0)
            {
                count=1;
                index=i;
            }
        }
        return num[index];
    }
};

int main()
{
    vector<int> num={3,3,3,3,3,3,1,2,4,5,3,45,2,54};
    Solution s;
    cout<<s.majorityElement(num)<<endl;
}

 

#include<iostream>
#include<vector>
using namespace std;

class Solution {
public:
    int majorityElement(vector<int> &num) {
        if(num.empty())
            return -1;
        int n=num.size();
        int major=num[0];
        int i;
        int count=1;
        for(i=1;i<n;i++)
        {
            if(num[i]==major)
                count++;
            else
                count--;
            if(count<0)
            {
                count=1;
                major=num[i];
            }
        }
        return major;
    }
};

int main()
{
    vector<int> num={3,3,3,3,3,3,1,2,5,3,45,2,54};
    Solution s;
    cout<<s.majorityElement(num)<<endl;
}

 若是要找當好出現一半的數呢？此時這個數多是經過上面的辦法找到的那個數，也多是最後一個數，所以，只須要再次遍歷數組，找出與最後一個數相等的數的個數，若是小於一半，那麼上面找出的數就是恰好出現一半的數，不然最後一個數是恰好出現一半的數。