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筛法求质

Posted by yc5_yc at 2012-06-15 21:37:44 on Problem 2262
这题把我写毛了!
几个重点,总结一下:
1、筛法求质
for(int i=2;i<1000000;i++)
        if(!A[i])
            for(int j=2*i;j<=1000000;j+=i)
                A[j]=1;
    A[0]=A[1]=1;
2、题目层次的优化(极其重要!)
for(i=3;i<=N/2;i+=2)
        {
            if(!(A[i]) && !(A[N-i]))
            {
                    printf("%d = %d + %d\n",N,i,N-i);
                    break;
            }
        }
还有几个细节问题,如筛法中的

    A[0]=A[1]=1;
还有
for(int i=2;i<1000000;i++)
第一次我想自作聪明地写成了
for(int i=2;i<600000;i++)
以上问题造成了18次WA+TLE的教训!

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