HDU 2098 分拆素数和

 

http://acm.hdu.edu.cn/showproblem.php?pid=2098

 

解题思路：打表打出10000以内素数，然后把素数放入到arr数组中，然后看n-arr[i]是不是素数并且不和n-arr[i]值相等，注意每种情况会算两遍，所以要除2。

 

#include <iostream>#include <stdio.h>#include <cmath>#include <string>#define MAX 10001using namespace std;void GetPrime(int Prime[]) { int i,j,qrt; for (i=4;i<=MAX;i+=2) Prime[i] = 1; qrt = sqrt(MAX); for (i=3;i<=qrt;i++) for(j=i*i;j<=MAX;j+=i) { if (Prime[j] == 1) continue; Prime[j] = 1; } }int main(){int Prime[MAX+5];int i,n,len=0;int count;int tem;int arr[MAX+5];memset(Prime,0,sizeof(Prime));Prime[1]=1;GetPrime(Prime);for (i=2;i<MAX;i++){if(Prime[i]==0)arr[len++]=i;}while (scanf("%d",&n)!=EOF&&n){count=0;for (i=0;i<len;i++){tem=n-arr[i];if(tem>0){if(Prime[tem]==0&&arr[i]!=tem)count++;}elsebreak;}cout<<count/2<<endl;}return 0;}