Contest1390 - 2018年第三阶段个人训练赛第五场.Make a Rectangle（水题）

问题 A: Make a Rectangle

时间限制: 1 Sec  内存限制: 128 MB
提交: 617  解决: 184
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题目描述

We have N sticks with negligible thickness. The length of the i-th stick is Ai.
Snuke wants to select four different sticks from these sticks and form a rectangle (including a square), using the sticks as its sides. Find the maximum possible area of the rectangle.

Constraints
4≤N≤105
1≤Ai≤109
Ai is an integer.

输入

Input is given from Standard Input in the following format:
N
A1 A2 ... AN

输出

Print the maximum possible area of the rectangle. If no rectangle can be formed, print 0.

样例输入

6
3 1 2 4 2 1

样例输出

2

提示

1×2 rectangle can be formed.

参考代码：

#include<iostream>
#include<algorithm>
using namespace std;
int main()
{
    int N;
    while(cin>>N)
    {
        long long a[N+10];
        for(int i=0; i<N; i++) cin>>a[i];
        sort(a,a+N);
        long long cnt=0,n,m;
        for(int i=N-1; i>0; i--)
        {
            if(a[i]==a[i-1])
            {
                cnt++,i--;
                if(cnt==1) n=a[i];
                if(cnt==2){
                    m=a[i];
                    break;
                }
            }
        }
        if(cnt==2) cout<<n*m<<endl;
        else cout<<0<<endl;
    }
}