Codeforces 1038D. Slime(思维)

#include <bits/stdc++.h>
#define maxn 500005
#define ll long long
using namespace std;
int n;
ll pre[maxn];

int main()
{
  scanf("%d",&n);
  int flag = 0;
  ll ans = 0;
  ll Min = 0x3f3f3f3f;
  ll Max = -0x3f3f3f3f;
  for(int i=0;i<n;i++){
    scanf("%lld",&pre[i]);
    ans += abs(pre[i]);
    Min = min(Min, pre[i]);
    Max = max(Max, pre[i]);
  }
  if(n == 1){
    cout<<pre[0]<<endl;
    return 0;
  }
  if(n == 2){
    cout<<max(pre[0] - pre[1],pre[1] - pre[0])<<endl;
    return 0;
  }
  if(Min > 0) ans -= 2 * Min;
  else if(Max < 0) ans -= 2 * abs(Max);
  cout<<ans<<endl;
  return 0;
}