题目链接:http://codeforces.com/problemset/problem/546/D
输入t对数 a, b
求(b,a]内的每个数拆成素因子的个数和
这里每个数都可以写成素数的乘积,可以写成几个素数的和就有几个素因子,这里求的是(b,a]内的素因子和
思路:
素数的素因子个数是1
对于非素数A的素因子个数 = A/k + 1 其中k是素数,也是第一个素数,或者K是比A小的数,并且A%k==0
下面是利用K是比A小的数,并且A%k==0
1 void solve(){ 2 Scanner sc = new Scanner(System.in); 3 int t = sc.nextInt(); 4 int a ,b; 5 int MAX = 5000000; 6 int[] arr=new int[MAX+1]; 7 for(int i=2;i<=MAX;i++){ 8 if(i%2==0){ 9 arr[i] = arr[i/2]+1; 10 continue; 11 } 12 for(int j=3;j*j<=i;j+=2){ 13 int k=i/j; 14 if(k*j==i){ 15 arr[i] = arr[k] + 1; 16 break; 17 } 18 } 19 if (arr[i]==0) 20 arr[i] = 1; 21 } 22 for(int i=2;i<=MAX;i++) 23 arr[i]+=arr[i-1]; 24 while(t!=0){ 25 a = sc.nextInt(); 26 b = sc.nextInt(); 27 System.out.println(arr[a]-arr[b]); 28 t--; 29 } 30 }
这个读数据效率低,造成运行时间超时
这个是利用素数的,找到第一个素数K,并且A%k==0
void solve3() throws NumberFormatException, IOException{ int limit = 5000005; BufferedReader br=new BufferedReader(new InputStreamReader(System.in)); int t=Integer.parseInt(br.readLine()); StringTokenizer st; int div[] = new int[limit]; boolean isPrime[] = new boolean[limit]; int prime[] = new int[limit]; int p=0; for(int i=2;i<limit;i++){ if(!isPrime[i]) prime[p++]=i; for(int j=0;j<p &&i*prime[j]<limit;j++){ isPrime[i*prime[j]] = true; if(i%prime[j]==0) break; } } for(int i=2;i<limit;i++){ int k = i; if(!isPrime[i]){ div[i] = 1; continue; } for(int j=0;j<p;j++){ if(k%prime[j]==0){ div[i] = div[k/prime[j]] + 1; break; } } } for(int i=2;i<limit;i++) div[i] += div[i-1]; StringBuilder sb=new StringBuilder(); for(int i=0;i<t;i++){ st=new StringTokenizer(br.readLine()); int a=Integer.parseInt(st.nextToken()); int b=Integer.parseInt(st.nextToken()); sb.append(div[a]-div[b]); sb.append(‘\n‘); } System.out.print(sb); }
换了读数据的方式,成功通过,这里利用到,素数筛选法求出素数的集合
还有下面一种,都是参考素数筛选法的求解
void solve2() throws NumberFormatException, IOException{ BufferedReader br=new BufferedReader(new InputStreamReader(System.in)); int t=Integer.parseInt(br.readLine()); StringTokenizer st; int limit = 5000000; boolean[] array = new boolean[limit+1]; int div[] = new int[limit+1]; for(int i=2;i<=limit;i++){ if(array[i]) continue; for(int j=i;j<=limit;j+=i){ array[j] = true; int k=j; int temp=0; while(k%i==0){ k/=i; temp++; } div[j]+=temp; } } for(int i=1;i<=limit;i++) div[i]+=div[i-1]; StringBuilder sb=new StringBuilder(); for(int i=0;i<t;i++){ st=new StringTokenizer(br.readLine()); int a=Integer.parseInt(st.nextToken()); int b=Integer.parseInt(st.nextToken()); sb.append(div[a]-div[b]); sb.append(‘\n‘); } System.out.print(sb); }
全部程序如下
package codeforces; import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; import java.util.*; public class D546 { void run() throws NumberFormatException, IOException{ // solve();// 超时 solve3(); } void solve3() throws NumberFormatException, IOException{ int limit = 5000005; BufferedReader br=new BufferedReader(new InputStreamReader(System.in)); int t=Integer.parseInt(br.readLine()); StringTokenizer st; int div[] = new int[limit]; boolean isPrime[] = new boolean[limit]; int prime[] = new int[limit]; int p=0; for(int i=2;i<limit;i++){ if(!isPrime[i]) prime[p++]=i; for(int j=0;j<p &&i*prime[j]<limit;j++){ isPrime[i*prime[j]] = true; if(i%prime[j]==0) break; } } for(int i=2;i<limit;i++){ int k = i; if(!isPrime[i]){ div[i] = 1; continue; } for(int j=0;j<p;j++){ if(k%prime[j]==0){ div[i] = div[k/prime[j]] + 1; break; } } } for(int i=2;i<limit;i++) div[i] += div[i-1]; StringBuilder sb=new StringBuilder(); for(int i=0;i<t;i++){ st=new StringTokenizer(br.readLine()); int a=Integer.parseInt(st.nextToken()); int b=Integer.parseInt(st.nextToken()); sb.append(div[a]-div[b]); sb.append(‘\n‘); } System.out.print(sb); } void solve2() throws NumberFormatException, IOException{ BufferedReader br=new BufferedReader(new InputStreamReader(System.in)); int t=Integer.parseInt(br.readLine()); StringTokenizer st; int limit = 5000000; boolean[] array = new boolean[limit+1]; int div[] = new int[limit+1]; for(int i=2;i<=limit;i++){ if(array[i]) continue; for(int j=i;j<=limit;j+=i){ array[j] = true; int k=j; int temp=0; while(k%i==0){ k/=i; temp++; } div[j]+=temp; } } for(int i=1;i<=limit;i++) div[i]+=div[i-1]; StringBuilder sb=new StringBuilder(); for(int i=0;i<t;i++){ st=new StringTokenizer(br.readLine()); int a=Integer.parseInt(st.nextToken()); int b=Integer.parseInt(st.nextToken()); sb.append(div[a]-div[b]); sb.append(‘\n‘); } System.out.print(sb); } void solve(){ Scanner sc = new Scanner(System.in); int t = sc.nextInt(); int a ,b; int MAX = 5000000; int[] arr=new int[MAX+1]; for(int i=2;i<=MAX;i++){ if(i%2==0){ arr[i] = arr[i/2]+1; continue; } for(int j=3;j*j<=i;j+=2){ int k=i/j; if(k*j==i){ arr[i] = arr[k] + 1; break; } } if (arr[i]==0) arr[i] = 1; } for(int i=2;i<=MAX;i++) arr[i]+=arr[i-1]; while(t!=0){ a = sc.nextInt(); b = sc.nextInt(); System.out.println(arr[a]-arr[b]); t--; } } public static void main(String[] args) throws NumberFormatException, IOException { new D546().run(); } }
时间: 2024-10-22 10:24:13