绝对值最小

#include <iostream>
#include <algorithm>
#define max 100005
#define ll long long
using namespace std;
ll a[max];

ll ab(ll a){
    if(a>=0)return a;
    else return -a;
}
int main()
{
    int n;
    while(cin>>n){
        for(ll i = 0;i < n;i++){
            cin>>a[i];
        }
        sort(a,a+n);///对整个数组进行着一个排序
        ll  ans = 0,index = 0;
        for(ll i = 0;i < n;i++){
            if(ab(a[i]-0)<ab(a[index]-0))index = i;
        }
        ans = ab(2 * a[index]);
        for(ll i = 0;i <= index;i++){
            for(ll j = n-1;j >= index;j--){
                if(abs(a[i]+a[j])<ans)ans = ab(a[i]+a[j]);
            }
        }
        cout<<ans<<endl;
    }
    return 0;
}