题解：https://www.zybuluo.com/jesseliu612/note/668669
1 #include<cmath> 2 #include<queue> 3 #include<cstdio> 4 #include<vector> 5 #include<cstdlib> 6 #include<cstring> 7 #include<iostream> 8 #include<algorithm> 9 #define N 100010 10 #define RG register 11 #define inf 0x3f3f3f3f 12 #define Inf 99999999999999999LL 13 using namespace std; 14 typedef long long LL; 15 bool vis[N]; 16 LL ans,anss,fix[N]; 17 int n,m,loc,top,nowloc,mu[N],pre[N],sta[N]; 18 inline int Abs(RG const int &a){return a>0?a:-a;} 19 inline int Max(RG const int &a,RG const int &b){return a>b?a:b;} 20 inline int Min(RG const int &a,RG const int &b){return a>b?b:a;} 21 inline int gi(){ 22 RG int x=0;RG bool flag=0;RG char c=getchar(); 23 while((c<'0'||c>'9')&&c!='-') c=getchar(); 24 if(c=='-') c=getchar(),flag=1; 25 while(c>='0'&&c<='9') x=x*10+c-'0',c=getchar(); 26 return flag?-x:x; 27 } 28 inline void init(){ 29 mu[1]=pre[1]=1; 30 for (RG int i=2;i<=n;++i){ 31 if(!vis[i]){ 32 mu[i]=-1; 33 sta[++top]=i; 34 } 35 for (RG int j=1;j<=top&&i*sta[j]<=n;++j){ 36 vis[i*sta[j]]=1; 37 if(i%sta[j]==0){ 38 mu[i*sta[j]]=0; 39 break; 40 } 41 mu[i*sta[j]]=-mu[i]; 42 } 43 pre[i]=pre[i-1]+mu[i]; 44 } 45 } 46 inline void coc(RG int aa,RG int bb){ 47 anss=0; 48 for (RG int i=1;i<=aa;i=loc+1){ 49 loc=Min(aa/(aa/i),bb/(bb/i)); 50 anss+=(LL)(pre[loc]-pre[i-1])*(LL)(aa/i)*(LL)(bb/i); 51 } 52 } 53 inline void work(){ 54 n=gi();m=gi(); 55 if(n>m) swap(n,m); 56 init(); 57 for (RG int i=1;i<=n;++i) 58 fix[i]=fix[i-1]+i; 59 for (RG int i=1;i<=n;i=nowloc+1){ 60 coc(n/i,m/i); 61 nowloc=Min(n/(n/i),m/(m/i)); 62 ans+=(fix[nowloc]-fix[i-1])*anss; 63 } 64 printf("%lld ",ans*2-(LL)n*m); 65 } 66 int main(){ 67 work(); 68 return 0; 69 }