【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

【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());

		}

	}

}