POJ 2909 Goldbach's Conjecture(简单题)
2014-09-24 16:44
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【题意简述】:输入一个数,输出有几对素数对可以使他们的和正好等于这个数
【分析】:暴力打表,再暴力循环求解
【分析】:暴力打表,再暴力循环求解
//268K 125Ms #include<iostream> using namespace std; #define N 35000 // 2^15 bool isprime ; int prime ,nprime;//prime 用来存储素数,nprime是此时一共有多少素数 void doprime(int n) { int i,j; nprime = 1; memset(isprime,true,sizeof(isprime)); isprime[1] = 0; prime[0] = 1; for(i = 2;i<=n;i++) { if(isprime[i]) { prime[nprime++] = i; for(j = i*i;j<=n;j+=i) { isprime[j] = false; } } } } int main() { int n; while(cin>>n,n) { int ans = 0; doprime(n); for(int i = 1;i<=nprime;i++) { for(int j = i;j<=nprime;j++) { if(n == prime[i]+prime[j]) ans++; } } cout<<ans<<endl; } return 0; }
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