題意：

給一個(gè)數(shù)n，問1~n內(nèi)有多少個(gè)素?cái)?shù)

題目：

Write a program which reads an integer n and prints the number of prime numbers which are less than or equal to n. A prime number is a natural number which has exactly two distinct natural number divisors: 1 and itself. For example, the first four prime numbers are: 2, 3, 5 and 7.

Input

Input consists of several datasets. Each dataset has an integer n (1 ≤ n ≤ 999,999) in a line.

The number of datasets is less than or equal to 30.

Output

For each dataset, prints the number of prime numbers.

Sample Input

10
3
11

Output for the Sample Input

4
2
5

分析：

打個(gè)素?cái)?shù)篩就行

AC模板：

#include<stdio.h> #include<string.h> #include<map> #include<algorithm> using namespace std; const int M=1e6+10; int n; int dp[M],book[M]; map<int,int>mp; void init() {for(int i=2; i<M; i++){if(!book[i]){mp[i]=1;for(int j=i; j<M; j+=i)book[j]=1;}}for(int i=1; i<M; i++){dp[i]=dp[i-1];if(mp[i])dp[i]++;} } int main() {init();while(~scanf("%d",&n)){printf("%d\n",dp[n]);}return 0; }

備戰(zhàn)ccpc分站賽ing ，題目分析簡(jiǎn)略，見諒，轉(zhuǎn)載請(qǐng)注明出處。。。。。

總結(jié)

以上是生活随笔為你收集整理的Prime Number Aizu - 0009（素数筛）的全部?jī)?nèi)容，希望文章能夠幫你解決所遇到的問題。

如果覺得生活随笔網(wǎng)站內(nèi)容還不錯(cuò)，歡迎將生活随笔推薦給好友。