UVA 506 System Dependencies（模拟 烂题）

https://vjudge.net/problem/UVA-506

　　题目是给出了五种指令，DEPEND、INSTALL、REMOVE、LIST、END，操作的格式及功能如下：

　　INSTALL指令中作为参数的组件的安装是显式安装，其所依赖的组件的安装不是显示安装。被显式安装的组件只能通过REMOVE指令显式删除，而移除中的组件如果当前被其他显式安装的组件直接或间接地依赖，则不能通过REMOVE移除。

　　每当输入指令之后，先原样输出一遍指令，然后执行指令。安装组件时如果可以安装组件则需输出“Installing
组建名”。如果显式安装时组件已被安装则提示“组建名 is already
installed.”，隐式安装则无需提示。如果显式删除组件时组件未被安装则提示“组建名 is not
installed.”，如果组件被其他组件依赖则提示“组建名 is still needed.”，隐式卸载则无需提示。

　　其实就是个用STL做的复杂模拟，纯属吃力不讨好的题目，并学不到什么算法思想，唯一的亮点就是为一个组件建立依赖和被依赖两个列表，其他的操作模拟即可。

 1 #include <iostream>
 2 #include <algorithm>
 3 #include <string>
 4 #include <sstream>
 5 #include <set>
 6 #include <vector>
 7 #include <stack>
 8 #include <map>
 9 #include <queue>
10 #include <deque>
11 #include <cstdlib>
12 #include <cstdio>
13 #include <cstring>
14 #include <cmath>
15 #include <ctime>
16 #include <functional>
17 using namespace std;
18
19 int cnt = 0, status[maxn];
20 vector<int> depend[maxn], depend2[maxn];
21 vector<int> installed;
22 string name[maxn];
23
24 int get_id(const string & x)
25 {
26     for (int i = 0; i < cnt; i++)
27         if (name[i] == x)
28             return i;
29     name[cnt++] = x;
30     return cnt-1;
31 }
32
33 void instal(int item, bool top)
34 {
35     if (!status[item]){
36         for (size_t i = 0; i < depend[item].size(); i++)
37             instal(depend[item][i], false);
38         cout << "   Installing " << name[item] << endl;
39         status[item] = top ? 1 : 2;
40         installed.push_back(item);
41     }
42     else if(top)
43         cout << "   " << name[item] << " is already installed." << endl;
44 }
45
46 bool needed(int item)
47 {
48     for (size_t i = 0; i < depend2[item].size(); i++)
49         if (status[depend2[item][i]])
50             return true;
51     return false;
52 }
53
54 void Remove(int item, bool top)
55 {
56     if(top && status[item]==0)
57         cout << "   " << name[item] << " is not installed." << endl;
58     else if(top && needed(item))
59         cout << "   " << name[item] << " is still needed." << endl;
60     else if ((top || status[item] == 2) && !needed(item)){
61         status[item] = 0;
62         installed.erase(remove(installed.begin(), installed.end(), item), installed.end());
63         cout << "   Removing " << name[item] << endl;
64         for (size_t i = 0; i < depend[item].size(); i++)
65             Remove(depend[item][i], false);
66     }
67 }
68
69 int main()
70 {
72     ios::sync_with_stdio(false);
73     string line;
74     while (getline(cin, line), line != "END")
75     {
76         cout << line << endl;
77         stringstream ss(line);
78         if (line[0] == ‘L‘){
79             for (size_t i = 0; i != installed.size(); ++i)
80                 cout << "   " << name[installed[i]] << endl;
81         }
82         else{
83             string t1, t2, t3;
84             ss >> t1 >> t2;
85             if (t1[0] == ‘D‘){
86                 while (ss >> t3){
87                     depend[get_id(t2)].push_back(get_id(t3));
88                     depend2[get_id(t3)].push_back(get_id(t2));
89                 }
90             }
91             else if (t1[0] == ‘I‘)
92                 instal(get_id(t2), true);
93             else if (t1[0] == ‘R‘)
94                 Remove(get_id(t2), true);
95         }
96     }
97     cout << "END" << endl;
98     return 0;
99 }