题意有点不明白，因为MAX为int最大值，推测为64位，AC
#include <cstdio>
#include <iostream>
#include <cstring>
#include <cctype>
#include <algorithm>
#define LL __int64
using namespace std;
const LL MAX=2147483647;
const int N=110;
LL friends[N];
int n;LL tot;
struct Node{
LL v,c;
}node[N];
bool cmp(LL a,LL b){
if(a<b) return true;
return false;
}
int main(){
int t=0;
while(scanf("%d",&n)!=EOF){
tot=-1;
for(int i=0;i<n;i++){
scanf("%I64d",&friends[i]);
node[i].c=0;
}
sort(friends,friends+n,cmp);
for(int i=0;i<n;i++){
if(i==0||friends[i]!=friends[i-1]){
node[++tot].v=friends[i];
node[tot].c++;
}
else if(friends[i]==friends[i-1])
node[tot].c++;
}
if(tot==0){
printf("Case #%d: -1
",++t);
continue;
}
LL now,le,rig; tot++;
LL ans=0;
for(LL i=0;i<tot;i++){
now=i;
le=((i-1)%tot+tot)%tot,rig=((i+1)%tot+tot)%tot;
if((node[now].v+node[le].v)%MAX==node[rig].v)
ans+=node[now].c;
}
printf("Case #%d: %I64d
",++t,ans);
}
return 0;
}