zoj 2723 Semi-Prime(set)

Semi-Prime

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Time Limit: 2 Seconds      Memory Limit: 65536 KB

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Prime Number Definition 
An integer greater than one is called a prime number if its only positive divisors (factors) are one and itself. For instance, 2, 11, 67, 89 are prime numbers but 8, 20, 27 are not.

Semi-Prime Number Definition 
An integer greater than one is called a semi-prime number if it can be decompounded to TWO prime numbers. For example, 6 is a semi-prime number but 12 is not.

Your task is just to determinate whether a given number is a semi-prime number.

Input

There are several test cases in the input. Each case contains a single integer N (2 <= N <= 1,000,000)

Output

One line with a single integer for each case. If the number is a semi-prime number, then output "Yes", otherwise "No".

Sample Input

3
4
6
12

Sample Output

No
Yes
Yes
No

建立素数表和半素数表，建立半素数表是通过素数表中的任意两个素数相乘得到保存起来。

 #include <iostream>
 #include <vector>
 #include <set>
 #include <cmath>
 using namespace std;
 //建立全局向量，用来保存素数
 vector<int> v;
 //在全局内存中定义全局集合容器，用来保存半素数
 //集合是平衡二叉检索树，搜索速度最快
 set<int> s;
 //建立[a, b]范围内素数表
 void pt(int a, int b){
     for(int i = a; i <= b; i++){
         //2是素数，清除2的倍数
         if(i !=  && i %  == ) continue;
         //消除素数的倍数
         for(int j = ; j * j <= i; j += ){
             if(i % j == )
                 goto RL;
         }
         v.push_back(i);
         RL: continue;
     }
 }

 int main(){
     pt(, );
     int i, j, p;
     for(i = ; i < v.size(); i++){
         for(j = ; j < v.size(); j++){
             p = v[i] * v[j];
             if(p < )
                 s.insert(p);
             else
                 break;
         }
     }
     //读入数据，在半素数表中查找，看是否在该表
     int n;
     set<int>::iterator it;
     while(cin >> n){
         it = s.find(n);
         if(it != s.end())
             cout << "Yes" << endl;
         else
             cout << "No" << endl;
     }
     return ;
 }