题目链接如下：

Online Judge

这道题有个小细节，explicitly installed的component，不能被implicitly removed. 

有一点拓扑排序的思想，用in[component]代表目前depend on在这个component上的component数量。

我的代码如下：

#include <iostream>
#include <string>
#include <map>
#include <vector>
#include <set>
#include <sstream>
// #define debugstruct node{std::string str;bool expli;bool exist = true;node(std::string _str): str(_str){}
};
std::string line, op, u, v;
std::map<std::string, int> in;
std::map<std::string, std::vector<std::string>> dep;
std::set<std::string> st;
std::vector<node> vec;
std::map<std::string, int> mp;void install(std::string str, bool flag){for (int i = 0; i < dep[str].size(); ++i){if (st.find(dep[str][i]) == st.end()){install(dep[str][i], false);}in[dep[str][i]]++;}printf("   Installing %s\n", str.c_str());st.insert(str);mp[str] = vec.size();vec.push_back(node(str));vec.back().expli = flag;
}void remove(std::string str){printf("   Removing %s\n", str.c_str());st.erase(str);vec[mp[str]].exist = false;for (int i = 0; i < dep[str].size(); ++i){in[dep[str][i]]--;if (!in[dep[str][i]] && !vec[mp[dep[str][i]]].expli){remove(dep[str][i]);}}
}int main(){#ifdef debugfreopen("0.txt", "r", stdin);freopen("1.txt", "w", stdout);#endifwhile (getline(std::cin, line)){in.clear();dep.clear();st.clear();vec.clear();mp.clear();do {printf("%s\n", line.c_str());std::stringstream ss(line);ss >> op;if (op == "LIST"){for (int i = 0; i < vec.size(); ++i){if (vec[i].exist){printf("   %s\n", vec[i].str.c_str());}}} else {ss >> u;if (op == "DEPEND"){while (ss >> v){dep[u].push_back(v);}} else if (op == "INSTALL"){if (st.find(u) != st.end()){printf("   %s is already installed.\n", u.c_str());} else {install(u, true);}} else if (op == "REMOVE"){if (st.find(u) == st.end()){printf("   %s is not installed.\n", u.c_str());} else if (in[u]) {printf("   %s is still needed.\n", u.c_str());} else {remove(u);}}}getline(std::cin, line);} while (line[0] != 'E');printf("%s\n", line.c_str());}#ifdef debugfclose(stdin);fclose(stdout);#endifreturn 0;
}