【Codeforces 385C】Bear and Prime Numbers

【链接】 我是链接,点我呀:)
【题意】

f[i]表示在x[]中有多少个数字是i的倍数
让你求出sum(f[i]) li<=i<=ri 且i是质数

【题解】

做筛法求素数的时候顺便把素数i在x[]中的倍数的个数求出来就好
前缀和 输出即可

【代码】

import java.io.*;
import java.util.*;

public class Main {
    
    
    static InputReader in;
    static PrintWriter out;
        
    public static void main(String[] args) throws IOException{
        //InputStream ins = new FileInputStream("E:\\rush.txt");
        InputStream ins = System.in;
        in = new InputReader(ins);
        out = new PrintWriter(System.out);
        //code start from here
        new Task().solve(in, out);
        out.close();
    }
    
    static int N = (int)1e7;
    static class Task{
        public void solve(InputReader in,PrintWriter out) {
            int n;
            int []cnt = new int [N+10];
            int []shai = new int [N+10];
            long []f = new long [N+10];
            n = in.nextInt();
            for (int i = 1;i <= n;i++) {
                int x;
                x = in.nextInt();
                cnt[x]++;
            }
            
            for (int i = 2;i <= N;i++)
                if (shai[i]==0) {
                    f[i] = cnt[i];
                    for (int j = 2*i;j <= N;j+=i) {
                        f[i] = f[i] + cnt[j];
                        shai[j] = 1;
                    }
                }
            for (int i = 1;i <= N;i++)
                f[i]=f[i-1]+f[i];
            n = in.nextInt();
            for (int i = 1;i <= n;i++) {
                int l,r;
                l = in.nextInt();r = in.nextInt();
                l = Math.min(l, N);r = Math.min(r,N);
                out.println(f[r]-f[l-1]);
            }
        }
    }

    

    static class InputReader{
        public BufferedReader br;
        public StringTokenizer tokenizer;
        
        public InputReader(InputStream ins) {
            br = new BufferedReader(new InputStreamReader(ins));
            tokenizer = null;
        }
        
        public String next(){
            while (tokenizer==null || !tokenizer.hasMoreTokens()) {
                try {
                tokenizer = new StringTokenizer(br.readLine());
                }catch(IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }
        
        public int nextInt() {
            return Integer.parseInt(next());
        }
    }
}