POJ-2799（找到一组IP的最小网络）

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题目：http://poj.org/problem?id=2799

思路：找出IP的最长公共前缀即最小网络，长度即子网掩码全1的长度

#include <cstdio>#define MAX1005int main(){unsigned n, i, a, b, c, d, ip, net;int len;while(scanf("%u", &n) == 1){scanf("%u.%u.%u.%u", &a, &b, &c, &d);net = a << 24 | b << 16 | c << 8 | d;len = 32;for(i = 1; i < n; ++i){scanf("%u.%u.%u.%u", &a, &b, &c, &d);ip = a << 24 | b << 16 | c << 8 | d;//find longest common prefix between ip and netint b = 31;for(; b >= 32-len; --b){if((net & (1u << b)) ^ (ip & (1u << b))) break;}//update common prefixlen = 31 - b;}//first len bits are 1unsigned mask = 0;for(int b = 31; b >= 32-len; --b) mask |= 1 << b;net &= mask;printf("%u.%u.%u.%u\n", net >> 24 & 255, net >> 16 & 255, net >> 8 & 255, net & 255);printf("%u.%u.%u.%u\n", mask >> 24 & 255, mask >> 16 & 255, mask >> 8 & 255, mask & 255);}return 0;}

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