UVA - 506 System Dependencies(STL + 模拟)

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组件之间具有依赖关系，模拟实现组建的安装和删除操作。

指令	说明
DEPEND item1 item2 [item3 …]	安装item1需要先安装item2（、item3……）
INSTALL item1	安装item1和它的依赖(已安装过的不用安装)
REMOVE item1	移除item1及其依赖的全部组件，如果组件被其他程序依赖，则不移除
LIST	输出当前已安装的所有组件

*STL中的remove(begin(), end(), t) 是找到第一个t位置，后面非t的元素前移，使得所有t被覆盖，并返回最后一个有用的位置，容器大小不变，再通过erase操作删除没用的区间即可。
代码:

#include<bits/stdc++.h>

using namespace std;
const int maxn = 1e5;
map<string, int> id;
vector<int> depend[maxn];
vector<int> depend2[maxn];
vector<int> installed;
int status[maxn];
string name[maxn];
int cnt;

int getId(string s) {
    if(id.count(s)) return id[s];
    id[s] = ++cnt;
    name[cnt] = s;
    return cnt;
}

void _install(int item, int toplevel) {
    if(status[item] && toplevel) {
        cout << "   " << name[item] << " is already installed." << endl;
        return;
    }
    if(!status[item]) {
        for(int i = 0; i < depend[item].size(); i++) {
            _install(depend[item][i], 0);
        }
        cout << "   Installing " << name[item] << endl;
        status[item] = toplevel ? 1 : 2;
        installed.push_back(item);
    }
    return;
}

int needed(int item) {
    for(int i = 0; i < depend2[item].size(); i++) {
        if(status[depend2[item][i]]) return 1;
    }
    return 0;
}

void _remove(int item, int toplevel) {
    if(!status[item] && toplevel) {
        cout << "   " << name[item] << " is not installed." << endl;
        return;
    }
    if(needed(item) && toplevel) {
        cout << "   " << name[item] << " is still needed." << endl;
        return;
    }
    if((toplevel || status[item] == 2) && !needed(item)) {
        status[item] = 0;
        installed.erase(remove(installed.begin(), installed.end(), item), installed.end());
        cout << "   Removing " << name[item] << endl;

        for(int i = 0; i < depend[item].size(); i++) _remove(depend[item][i], 0);
    }
    return;
}

void _list() {
    for(int i = 0; i < installed.size(); i++) cout << "   " << name[installed[i]] << endl;
    return;
}

int main() {
    ios::sync_with_stdio(false);
    //freopen("D:\\input.txt", "r", stdin);
    //freopen("D:\\output.txt", "w", stdout);
    string str;
    while(getline(cin, str)) {
        cout << str << endl;
        stringstream ss(str);
        string op, s;
        ss >> op;
        if(op == "END") break;
        if(op == "DEPEND") {
            ss >> s;
            int t = getId(s);
            while(ss >> s) {
                depend[t].push_back(getId(s));
                depend2[getId(s)].push_back(t);
            }
        }
        else if(op == "INSTALL") 
            while(ss >> s) _install(getId(s), 1);
        else if(op == "REMOVE") {
            ss >> s;
            _remove(getId(s), 1);
        }
        else if(op == "LIST") _list();
    }
    return 0;
}