Single Number

Given an array of integers, every element appears twice except for one. Find that single one.

Note:
Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory?

 

注意：多关键字的multimap不能使用下标操作。

C++代码如下：

#include<iostream>

#include<map>

using namespace std;



class Solution

{

public:

    int singleNumber(int A[],int n)

    {

        multimap<int,int> mp;

        int i;

        for(i=0;i<n;i++)

        {

            mp.insert({A[i],i});

        }

        auto map_it=mp.begin();

        while(map_it!=mp.end())

        {

            auto tmp=map_it;

            tmp++;

            if((tmp)==mp.end())

                return (map_it)->first;

            if(map_it->first!=(tmp)->first)

                break;

            map_it++;

            map_it++;

        }

        return map_it->first;

    }

};



int main()

{

    Solution s;

    int arr[]={2,4,2,4,5};

    cout<<s.singleNumber(arr,5)<<endl;

}

 

第二遍刷：

    int singleNumber(int A[],int n)

    {

        multiset<int> st;

        int i;

        for(i=0;i<n;i++)

            st.insert(A[i]);

        for(i=0;i<n;i++)

            if(st.count(A[i])!=2)

                break;

        return A[i];

    }