//预处理所有数的因数
//从前到后扫一遍，记录所有因子的最后一个位置，找出所有b[i]
//然后从后到前扫一遍，找出所有c[i]
#include<cstdio>
#include<cstring>
#include<iostream>
#include<vector>
#include<cmath>
using namespace std ;
const int maxn = 100010 ;
typedef __int64 ll ;
vector<int>vec[maxn] ;
int vis[maxn] ;
int a[maxn];
int b[maxn] ;
int c[maxn] ;
void init()
{
for(int i = 1;i < maxn;i++)
for(int j = 1;j <= (int)sqrt((double)i) ;j++)
{
if(i%j == 0)
{
vec[i].push_back(j) ;
if(j*j !=i)
vec[i].push_back(i/j) ;
}
}
}
int main()
{
int n ;
init() ;
while(~scanf("%d" ,&n) && n)
{
memset(vis , 0 , sizeof(vis)) ;
for(int i = 1;i <= n;i++)
{
scanf("%d" ,&a[i]) ;
if(!vis[a[i]])
b[i] = a[i] ;
else b[i] = vis[a[i]] ;
for(int j = 0;j < vec[a[i]].size() ;j++)
vis[vec[a[i]][j]] = a[i] ;
}
memset(vis , 0 ,sizeof(vis)) ;
ll ans = 0 ;
for(int i = n;i >= 1;i--)
{
if(!vis[a[i]])c[i] = a[i] ;
else c[i] = vis[a[i]] ;
for(int j = 0;j < vec[a[i]].size();j++)
vis[vec[a[i]][j]] = a[i] ;
ans += (ll)b[i]*(ll)c[i] ;
}
printf("%I64d\n" ,ans) ;
}
return 0 ;
}
//STL存入每一个数的每一个位置
//枚举所有点的倍数值
//二分找其位置
#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
#include<vector>
using namespace std;
const int maxn = 100010;
vector<int>vec[maxn] ;
typedef __int64 ll ;
int a[maxn] ;
int find_r(int i , int num)
{
int l = 0 ;
int r = vec[i].size() - 1 ;
while(l<=r)
{
int mid = (l+r) >> 1 ;
if(vec[i][mid] <= num)
l = mid + 1 ;
else r = mid - 1 ;
}
if(l < 0 || l >= vec[i].size())return -1;
return vec[i][l];
}
int find_l(int i , int num)
{
int l = 0;
int r = vec[i].size() - 1 ;
while(l <= r)
{
int mid = (l+r) >> 1 ;
if(vec[i][mid] >= num)
r = mid - 1;
else l = mid + 1;
}
if(r >= vec[i].size() || r < 0)
return -1 ;
return vec[i][r] ;
}
int main()
{
//freopen("in.txt","r",stdin) ;
int n ;
while(scanf("%d" ,&n) && n)
{
for(int i = 1;i < maxn;i++)
vec[i].clear() ;
for(int i = 1;i <= n;i++)
{
scanf("%d" ,&a[i]) ;
vec[a[i]].push_back(i) ;
}
for(int i = 1;i <= n;i++)
if(vec[i].size())
sort(vec[i].begin() , vec[i].end()) ;
ll ans = 0 ;
for(int i = 1;i <= n;i++)
{
int pos_r = i ,pos_l = i ;
if(a[i] == 1)
{
pos_l = i == 1 ? 1 : i-1 ;
pos_r = i == n ? n : i+1 ;
ans += (ll)a[pos_l]*(ll)a[pos_r] ;
continue;
}
for(int j = 1;;j++)
{
if(j*a[i] >= maxn)break;
if(!vec[j*a[i]].size())continue ;
int t_l = find_l(a[i]*j , i) ;
int t_r = find_r(a[i]*j , i) ;
if(t_l != -1)
pos_l = pos_l == i ? t_l : max(pos_l , t_l) ;
if(t_r != -1)
pos_r = pos_r == i ? t_r : min(pos_r , t_r) ;
}
ans+= (ll)a[pos_l]*(ll)a[pos_r] ;
}
printf("%I64d\n" ,ans) ;
}
return 0;
}
hdu4961
原文：http://blog.csdn.net/cq_pf/article/details/45849407
