POJ 2799 IP Networks
2015-03-23 20:44
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network address是前(32-n)随意 后n位全零
network mask是前(32-n)全一 后n位全零
本题主要利用位移操作,1ULL表示无符号长整型的常数1,这样写可防止不必要的溢出,取反后可以作为mask的枚举然后拿mask和mins或者maxs并一下就得到address了。
代码:
network mask是前(32-n)全一 后n位全零
本题主要利用位移操作,1ULL表示无符号长整型的常数1,这样写可防止不必要的溢出,取反后可以作为mask的枚举然后拿mask和mins或者maxs并一下就得到address了。
代码:
#include <cstdio> #include <iostream> using namespace std; const int maxn = 70; int main() { int n; while(scanf("%d", &n) == 1) { unsigned int maxs = 0; unsigned int mins = 0-1; //printf("%u\n",mins); int a, b, c, d; unsigned int e; for(int i = 0; i < n; i++) { scanf("%d.%d.%d.%d", &a, &b, &c, &d); e = ((unsigned int)a << 24) + (b << 16) + (c << 8) + d; //printf("%u\n",e); if(e < mins) mins = e; if(e > maxs) maxs = e; } unsigned int mask; for (int i = 0; i <= 32; i++) { mask = ~((1ULL<<i)-1U);//注意这里ULL,是为了防止数据溢出 //printf("%u\n",mask); if ((mins & mask) == (maxs & mask)) break; } unsigned int ans = mins & mask; printf("%u.%u.%u.%u\n", ans >> 24, (ans << 8) >> 24, (ans << 16) >> 24, (ans << 24) >> 24); printf("%u.%u.%u.%u\n", mask >> 24, (mask << 8) >> 24, (mask << 16) >> 24, (mask << 24) >> 24); } return 0; }
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