我是把ip地址转成32位的二进制，然后XOR，看到比较短的那个掩码的位数是不是都是0，但是只过了60多，不知道为什么。 #include <iostream> #include <cstdio> #include <map> #include <string> #include <sstream> #include <vector> #include <set> #include <bitset> using namespace std; ostringstream ostr; struct ip_addr { bitset<32> s1,s2,s3,s4; unsigned int l; bitset<32> bin; }; int main(){ int n= 0; cin >> n; vector<ip_addr> ips; vector<string> ipstring; set<int> idx; for(int i = 0; i < n; i++){ ip_addr ip; unsigned int s1,s2,s3,s4,l; scanf("%d.%d.%d.%d/%d",&s1,&s2,&s3,&s4,&ip.l); ip.s1 = bitset<32>(s1); ip.s2 = bitset<32>(s2); ip.s3 = bitset<32>(s3); ip.s4 = bitset<32>(s4); ip.bin = ((ip.s1<<8 | ip.s2)<<8 | ip.s3)<<8 | ip.s4; ips.push_back(ip); bool flag =false; for(auto j:idx){ ip_addr tmp = ips[j]; unsigned int tmp_l = tmp.l; bool current_wider = tmp.l>ip.l; unsigned int len = current_wider?ip.l:tmp.l; string compare="00000000000000000000000000000000"; string _xor = (tmp.bin^ip.bin).to_string(); if(compare.substr(0,len) == _xor.substr(0,len)){ if(current_wider){ idx.erase(j); } else{ flag = true; } } } if(flag){ continue; } idx.insert(i); } cout<<idx.size()<<endl; for(auto j:idx){ ip_addr ip = ips[j]; cout<<ip.s1.to_ulong()<<'.'<<ip.s2.to_ulong()<<'.'<<ip.s3.to_ulong()<<'.'<<ip.s4.to_ulong()<<'/'<<ip.l<<endl; } return 0; }