1.1 小于n的最大素数，完美立方

Love The Way You Lie 2022-05-11 00:26 206阅读 0赞

求小于n的最大素数（筛选法）

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#include<iostream>
    #include<cstring>
    #define MAXN 10000
    using namespace std;
    char isprime[MAXN];
    int main()
    {
    	int n;
    	cin >> n;
    	memset(isprime,1,sizeof(isprime));
    	//for(int i = 2; i <= n; ++i) isprime[i] = 1;
    	for(int i = 2; i <= n; ++i)
    	{
    		if(isprime[i])
    		{
    			for(int j = i*2; j <= n; j += i)
    				isprime[j] = 0;
    		}
    	}
    	for(int i = n; i >= 2; --i)
    	{
    		if(isprime[i])
    		{
    			cout << i << endl;
    			break;
    		}
    	}	
    	return 0;	
    }

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> b,c,d的值肯定没有a大，这里可以缩小一点范围。

#include<iostream>
    #include<cstdio>
    using namespace std;
    int main()
    {
    	int n, a, b, c, d;
    	scanf("%d",&n);
    	for(a = 2; a <= n; ++a)
    	{
    		for(b = 2; b < a; ++b)
    		{
    			for(c = b; c < a; ++c)
    			{
    				for(d = c; d < a; ++d)
    				{
    					if(a*a*a == b*b*b + c*c*c + d*d*d)
    					{
    						printf("Cube=%d,Triple=(%d,%d,%d)\n",a,b,c,d);
    					}
    				}
    			}
    		}
    	}
    	return 0;
    }

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