hdu 4961 Boring Sum
http://acm.hdu.edu.cn/showproblem.php?pid=4961
先打个表,把每个数的约数存起来,然后从前往后扫一遍,结果存在f[i],然后从后往前扫一遍,结果存在c[i],最后算f[i]*c[i]的和。
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
1 #include <cstdio> 2 #include <cstring> 3 #include <vector> 4 #include <algorithm> 5 #define maxn 100001 6 using namespace std; 7 8 int f[maxn],c[maxn]; 9 vector<int>g[maxn]; 10 int vis1[maxn],vis2[maxn]; 11 int a[maxn]; 12 void inti() 13 { 14 for(int i=2; i<=maxn; i++) 15 { 16 for(int j=i; j<=maxn; j+=i) 17 { 18 g[j].push_back(i); 19 } 20 } 21 } 22 int n; 23 int main() 24 { 25 inti(); 26 while(scanf("%d",&n)!=EOF) 27 { 28 memset(vis1,0,sizeof(vis1)); 29 memset(vis2,0,sizeof(vis2)); 30 memset(f,0,sizeof(f)); 31 memset(c,0,sizeof(c)); 32 memset(a,0,sizeof(a)); 33 if(n==0) break; 34 for(int i=1; i<=n; i++) 35 { 36 scanf("%d",&a[i]); 37 } 38 for(int i=1; i<=n; i++) 39 { 40 if(vis1[a[i]]==0) f[i]=a[i]; 41 else f[i]=vis1[a[i]]; 42 vis1[1]=a[i]; 43 for(int j=0; j<(int)g[a[i]].size(); j++) 44 { 45 vis1[g[a[i]][j]]=a[i]; 46 } 47 } 48 for(int i=n; i>=1; i--) 49 { 50 if(vis2[a[i]]==0) c[i]=a[i]; 51 else c[i]=vis2[a[i]]; 52 vis2[1]=a[i]; 53 for(int j=0; j<(int)g[a[i]].size(); j++) 54 { 55 vis2[g[a[i]][j]]=a[i]; 56 } 57 } 58 __int64 sum=0; 59 for(int i=1; i<=n; i++) 60 { 61 sum+=(__int64)f[i]*(__int64)c[i]; 62 } 63 printf("%I64d\n",sum); 64 } 65 return 0; 66 }