UVA 1590 IP Networks

题目链接：https://vjudge.net/problem/UVA-1590

题目翻译摘自《算法禁赛入门经典》

题目大意

　　给定 m 个 ip 地址，在尽量不浪费网络地址的情况下求包含这 m 个 ip 地址的最小网络地址和相应子网掩码。

分析

　　先定义 ip 地址之间的位运算，然后就好做了。

代码如下

#include <bits/stdc++.h>
using namespace std;
 
#define INIT() ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define Rep(i,n) for (int i = 0; i < (n); ++i)
#define For(i,s,t) for (int i = (s); i <= (t); ++i)
#define rFor(i,t,s) for (int i = (t); i >= (s); --i)
#define ForLL(i, s, t) for (LL i = LL(s); i <= LL(t); ++i)
#define rForLL(i, t, s) for (LL i = LL(t); i >= LL(s); --i)
#define foreach(i,c) for (__typeof(c.begin()) i = c.begin(); i != c.end(); ++i)
#define rforeach(i,c) for (__typeof(c.rbegin()) i = c.rbegin(); i != c.rend(); ++i)
 
#define pr(x) cout << #x << " = " << x << "  "
#define prln(x) cout << #x << " = " << x << endl
 
#define LOWBIT(x) ((x)&(-x))
 
#define ALL(x) x.begin(),x.end()
#define INS(x) inserter(x,x.begin())
 
#define ms0(a) memset(a,0,sizeof(a))
#define msI(a) memset(a,inf,sizeof(a))
#define msM(a) memset(a,-1,sizeof(a))

#define MP make_pair
#define PB push_back
#define ft first
#define sd second
 
template<typename T1, typename T2>
istream &operator>>(istream &in, pair<T1, T2> &p) {
    in >> p.first >> p.second;
    return in;
}
 
template<typename T>
istream &operator>>(istream &in, vector<T> &v) {
    for (auto &x: v)
        in >> x;
    return in;
}
 
template<typename T1, typename T2>
ostream &operator<<(ostream &out, const std::pair<T1, T2> &p) {
    out << "[" << p.first << ", " << p.second << "]" << "
";
    return out;
}

inline int gc(){
    static const int BUF = 1e7;
    static char buf[BUF], *bg = buf + BUF, *ed = bg;
    
    if(bg == ed) fread(bg = buf, 1, BUF, stdin);
    return *bg++;
} 

inline int ri(){
    int x = 0, f = 1, c = gc();
    for(; c<48||c>57; f = c=='-'?-1:f, c=gc());
    for(; c>47&&c<58; x = x*10 + c - 48, c=gc());
    return x*f;
}

template<class T>
inline string toString(T x) {
    ostringstream sout;
    sout << x;
    return sout.str();
}
 
typedef long long LL;
typedef unsigned long long uLL;
typedef pair< double, double > PDD;
typedef pair< int, int > PII;
typedef pair< int, PII > PIPII;
typedef pair< string, int > PSI;
typedef pair< int, PSI > PIPSI;
typedef set< int > SI;
typedef set< PII > SPII;
typedef vector< int > VI;
typedef vector< VI > VVI;
typedef vector< PII > VPII;
typedef map< int, int > MII;
typedef map< int, string > MIS;
typedef map< int, PII > MIPII;
typedef map< PII, int > MPIII;
typedef map< string, int > MSI;
typedef map< string, string > MSS;
typedef map< PII, string > MPIIS;
typedef map< PII, PII > MPIIPII;
typedef multimap< int, int > MMII;
typedef multimap< string, int > MMSI;
//typedef unordered_map< int, int > uMII;
typedef pair< LL, LL > PLL;
typedef vector< LL > VL;
typedef vector< VL > VVL;
typedef priority_queue< int > PQIMax;
typedef priority_queue< int, VI, greater< int > > PQIMin;
const double EPS = 1e-6;
const LL inf = 0x7fffffff;
const LL infLL = 0x7fffffffffffffffLL;
const LL mod = 1e9 + 7;
const int maxN = 1e3 + 7;
const LL ONE = 1;
const LL evenBits = 0xaaaaaaaaaaaaaaaa;
const LL oddBits = 0x5555555555555555;

struct IP{
    int ip[4] = {0};
    
    void allone() {
        Rep(i, 4) ip[i] = 255;
    }
    
    void allzero() {
        Rep(i, 4) ip[i] = 0;
    }
    
    void removeLowbit() {
        rFor(i, 3, 0) {
            if(ip[i] == 0) continue;
            ip[i] &= ip[i] - 1;
            break;
        }
    }
    
    bool isZero() {
        Rep(i, 4) if(ip[i]) return false;
        return true;
    }
    
    bool operator< (const IP &x) const {
        Rep(i, 4) if(ip[i] < x.ip[i]) return true;
        return false;
    }
    
    bool operator== (const IP &x) const {
        Rep(i, 4) if(ip[i] != x.ip[i]) return false;
        return true;
    }
    
    IP operator& (const IP &x) const {
        IP ret;
        Rep(i, 4) ret.ip[i] = ip[i] & x.ip[i];
        return ret;
    }
    
    IP operator| (const IP &x) const {
        IP ret;
        Rep(i, 4) ret.ip[i] = ip[i] | x.ip[i];
        return ret;
    }
    
    IP operator^ (const IP &x) const {
        IP ret;
        Rep(i, 4) ret.ip[i] = ip[i] ^ x.ip[i];
        return ret;
    }
    
    IP operator~ () const {
        IP ret;
        Rep(i, 4) ret.ip[i] = ~ip[i] & 0xff;
        return ret;
    }
};

istream &operator>> (istream &in, IP &x) {
    string tmp;
    in >> tmp;
    foreach(i, tmp) if(*i == '.') *i = ' ';
    stringstream sin(tmp);
    Rep(i, 4) sin >> x.ip[i];
    return in;
}

ostream &operator<< (ostream &out, const IP &x) {
    Rep(i, 4) {
        if(i) out << ".";
        out << x.ip[i];
    }
    out << endl;
    return out;
}

int m;
IP mask, allIP[maxN];

int main(){
    //freopen("MyOutput.txt","w",stdout);
    //freopen("input.txt","r",stdin);
    INIT();
    while(cin >> m) {
        mask.allone();
        
        Rep(i, m) {
            cin >> allIP[i];
            if(i) mask = ~(allIP[i - 1] ^ allIP[i]) & mask;
        }
        
        Rep(i, 4) {
            if(mask.ip[i] != 255) {
                For(j, i + 1, 3) mask.ip[j] = 0;
                Rep(j, 9) {
                    int x = (1 << j) - 1;
                    x = ~x & 0xff;
                    if((mask.ip[i] & x) == x) {
                        mask.ip[i] = x;
                        break;
                    }
                }
                break;
            }
        }
        
        cout << (allIP[0] & mask) << mask;
    }
    return 0;
}