1 // 题目链接 http://codeforces.com/contest/1006/problem/C 2 #include <iostream> 3 #include <cstdio> 4 #include <cstring> 5 #include <string> 6 #include <algorithm> 7 #include <utility> 8 #include <vector> 9 #include <map> 10 #include <queue> 11 #include <stack> 12 #include <cstdlib> 13 #include <deque> 14 #include <set> 15 typedef long long ll; 16 #define lowbit(x) (x&(-x)) 17 #define ls l,m,rt<<1 18 #define rs m+1,r,rt<<1|1 19 using namespace std; 20 map<ll,ll>mp; 21 map<ll,int>id; 22 int n; 23 const int N=2e5+9; 24 ll a[N]; 25 ll sum1[N],sum2[N]; 26 int main() 27 { //cout<<"njjni "; 28 scanf("%d",&n); 29 sum1[0]=0; 30 ll sum=0; 31 for(int i=1;i<=n;i++){ 32 scanf("%lld",&a[i]); 33 sum+=a[i]; 34 sum1[i]=sum1[i-1]+a[i]; 35 mp[sum1[i]]=1; 36 id[sum1[i]]=i; 37 } 38 /* 39 if(sum%2==0){ 40 printf("%lld ",sum/2); 41 return 0; 42 } 43 //上面的是错误的，例如 ： 44 1 1 45 2 46 就应该输出0 47 */ 48 sum2[n]=a[n]; 49 for(int i=n-1;i>=1;i--){ 50 sum2[i]=sum2[i+1]+a[i]; 51 52 } 53 ll maxx=0; 54 int i; 55 for(int j=n;j>=1;j--){ 56 if(mp[sum2[j]]==1){ 57 i=id[sum2[j]]; 58 if(i<j){ 59 //cout<<i<<" "<<j<<endl; 60 maxx=max(maxx,sum2[j]); 61 } 62 } 63 } 64 printf("%lld ",maxx); 65 return 0; 66 }