POJ 2909 Goldbach's Conjecture(素数表)
2010-06-13 20:39
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//这次是验证哥德巴赫猜想的解有多少个,同样核心是打素数表 //思路和POJ 2262差不多,筛法打素表 #include<iostream> using namespace std; const int MAXP = 400000; bool isPrime[MAXP]; int prime[MAXP]; void primeList() { memset(isPrime,true,sizeof(isPrime)); for(int i = 2;i <= MAXP;++i) { if(isPrime[i]) prime[++prime[0]] = i; for(int j = 1,k;(k = i * prime[j]) <= MAXP && j <= MAXP;++j) { isPrime[k] = false; if(i % prime[j] == 0) break; } } } int main() { primeList(); int n,ans; while(scanf("%d",&n) && n != 0) { ans = 0; for(int i = 1;prime[i] <= n/2;++i) { if(isPrime[n - prime[i]]) ++ans; } printf("%d/n",ans); } return 0; }
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