zoj 2723 Semi-Prime(set)

Semi-Prime

---

Time Limit: 2 Seconds      Memory Limit: 65536 KB

---

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 != 2 && i % 2 == 0) continue;
        //消除素数的倍数 
        for(int j = 3; j * j <= i; j += 2){
            if(i % j == 0)
                goto RL;
        }
        v.push_back(i);
        RL: continue;
    }
}

int main(){
    pt(2, 500000);
    int i, j, p;
    for(i = 0; i < v.size(); i++){
        for(j = 0; j < v.size(); j++){
            p = v[i] * v[j];
            if(p < 1000000)
                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 0;
}