Damn Single (25)

“Damn Single (單身狗)” is the Chinese nickname for someone who is being single. You are supposed to find those who are alone in a big party, so they can be taken care of.

Input Specification:

Each input file contains one test case. For each case, the first line gives a positive integer N (<=50000), the total number of couples. Then N lines of the couples follow, each gives a couple of ID’s which are 5-digit numbers (i.e. from 00000 to 99999). After the list of couples, there is a positive integer M (<=10000) followed by M ID’s of the party guests. The numbers are separated by spaces. It is guaranteed that nobody is having bigamous marriage (重婚) or dangling with more than one companion.

Output Specification:

First print in a line the total number of lonely guests. Then in the next line, print their ID’s in increasing order. The numbers must be separated by exactly 1 space, and there must be no extra space at the end of the line.

Sample Input:
3
11111 22222
33333 44444
55555 66666
7
55555 44444 10000 88888 22222 11111 23333
Sample Output:
5
10000 23333 44444 55555 88888

思路：pat甲級的一道題目，個人的第一次看到用map容器的用法，map的用法主要用于標記，這道題個人感覺很不錯，運用map，很好說明map的一些常用的用法。用法在代碼注釋。

#include <cstdio> #include <cstring> #include <vector> #include <map> #include <algorithm> #include <iostream> using namespace std; int main(){ int n,count=0; string a,b; map<string,string> c; map<string,int> d; vector<string> re; cin>>n; for(int i=1;i<=n;i++){ cin>>a>>b; c.insert(pair<string,string>(a,b));//對a和b進行插入，說明a是key，b是value；c.insert(pair<string,string>(b,a)); //想反的在進行一個插入，a與b此時連在一起的感覺。} cin>>n; for(int i=1;i<=n;i++){ cin>>a; d[a]=1; //對a進行標記；} int flag=0; map<string,int> ::iterator it; for(it=d.begin();it!=d.end();it++){ if(d.count(c[it->first])==0){ //count函數(shù)說明value有沒有出現(xiàn)，c【}it-》first 】的值是夫妻對方；主要要明白這里的it->first。count++; re.push_back(it->first); //map中的it->first是自動排序的。} } cout<<count<<endl; for(int i=0;i<re.size();i++){ cout<<re.at(i)<<(i==re.size()-1?'\n':' '); } return 0; }

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