ACM-ICPC 2018 南京賽區網路預賽-J Sum(線性篩選+因數分解)
A square-free integer is an integer which is indivisible by any square number except 11. For example, 6 = 2 \cdot 36=2⋅3 is square-free, but 12 = 2^2 \cdot 312=22⋅3 is not, because 2^222 is a square number. Some integers could be decomposed into product of two square-free integers, there may be more than one decomposition ways. For example, 6 = 1\cdot 6=6 \cdot 1=2\cdot 3=3\cdot 2, n=ab6=1⋅6=6⋅1=2⋅3=3⋅2,n=ab and n=ban=ba are considered different if a \not = ba̸=b. f(n)f(n) is the number of decomposition ways that n=abn=ab such that aa and bb are square-free integers. The problem is calculating \sum_{i = 1}^nf(i)∑i=1n f(i).
Input
The first line contains an integer T(T\le 20)T(T≤20), denoting the number of test cases.
For each test case, there first line has a integer n(n \le 2\cdot 10^7)n(n≤2⋅107).
Output
For each test case, print the answer \sum_{i = 1}^n f(i)∑i=1n f(i).
Hint
\sum_{i = 1}^8 f(i)=f(1)+ \cdots +f(8)∑i=18 f(i)=f(1)+⋯+f(8)
=1+2+2+1+2+4+2+0=14=1+2+2+1+2+4+2+0=14.
樣例輸入
2
5
8
樣例輸出
8
14
題解:可以將f(n)分解為:其中px為質數ex為指數;題目要求f(n)=a*b的對數,所以我們就可以可以判斷a的型別數量a可以由p1,p2,p3...px這些質因數中的一些乘積組成,按題目要求這些質因數我們只能選擇一個,所以對於每一個質因數假如指數都為1那麼每一個質因數選擇有兩種(選或不選),如果指數為2那就只能選著一個只有一種選法;
這樣我們就可以維護f[i*一個質數】;
#include<cstring> #include<cstdio> #include<iostream> #include<string> #include<queue> #include<vector> #include<algorithm> #include<cmath> #include<set> #include<map> #include<stack> #include<functional> using namespace std; #define eb(x) emplace_back(x) #define pb(x) push_back(x) #define ps(x) push(x) #define clr(a,b) memset(a,b,sizeof(a)) #define inf 0x3f3f3f3f3f3f3f3f3f3f #define MAX_N 20000000+5 #define MAX_M 13 typedef long long ll; const ll INF=10000000000000000LL; const ll maxn=2*1e7+2; typedef priority_queue<int,vector<int>,less<int> > pql; typedef priority_queue<int,vector<int>,greater<int> >pqg; /* 數學:線性篩選+因數分解規律 */ int tot,prime[maxn],vis[maxn],f[maxn]; ll res[maxn]; void init() { clr(prime,0); clr(vis,0); clr(res,0); prime[1]=1;res[1]=1;tot=0; for(int i=2;i<maxn;i++) { if(!vis[i])//新增到素數集合當中 { prime[tot++]=i; f[i]=2; } for(int j=0;j<tot&&i*prime[j]<maxn;j++)//乘每一個質數 { vis[i*prime[j]]=1; if(i%prime[j]==0) { if(i%(prime[j]*prime[j])==0){f[prime[j]*i]=0;}//指數超過2就代表為0 else f[prime[j]*i]=f[i]/2;//若果指數為2代表只有一種選法 break;//必須加只需查詢指數在2之內的就可以了 } else { f[prime[j]*i]=f[i]*2;//指數為1就*2 } } res[i]=res[i-1]+f[i]; } return ; } int main() { #ifndef ONLINE_JUDGE //freopen("data.txt","r",stdin); #endif init(); int t; scanf("%d",&t); while(t--) { int n; scanf("%d",&n); printf("%lld\n",res[n]); } return 0; }