UVa 506

这道题仍然是两个月之前做过，当时是RE，但不知为何当时没有考虑到把数组开的大一点就可以了。今天拿出代码将1024改为102400，瞬间AC。

网上搜了下竟然没有这个题的题解。我的做法还是很普通的做法，就是使用了STL的几个工具而已，比如vector、string、erase、remove、stringstream等等，没有算法上的难度。

#include <bits/stdc++.h>
#define maxn 102400
using namespace std;

int cnt = 0, status[maxn];
vector<int> depend[maxn], depend2[maxn];
vector<int> installed;
string name[maxn];

int get_id(const string & x)
{
	for (int i = 0; i < cnt; i++)
        if (name[i] == x)
            return i;
	name[cnt++] = x;
	return cnt-1;
}

void instal(int item, bool top)
{
	if (!status[item]){
		for (size_t i = 0; i < depend[item].size(); i++)
			instal(depend[item][i], false);
		cout << "   Installing " << name[item] << endl;
		status[item] = top ? 1 : 2;
		installed.push_back(item);
	}
	else if(top)
		cout << "   " << name[item] << " is already installed." << endl;
}

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

void Remove(int item, bool top)
{
    if(top && status[item]==0)
        cout << "   " << name[item] << " is not installed." << endl;
    else if(top && needed(item))
		cout << "   " << name[item] << " is still needed." << endl;
	else if ((top || status[item] == 2) && !needed(item)){
		status[item] = 0;
		installed.erase(remove(installed.begin(), installed.end(), item), installed.end());
		cout << "   Removing " << name[item] << endl;
		for (size_t i = 0; i < depend[item].size(); i++)
			Remove(depend[item][i], false);
	}
}

int main()
{
    //freopen("in.txt", "r", stdin);
    ios::sync_with_stdio(false);
	string line;
	while (getline(cin, line), line != "END")
	{
	    cout << line << endl;
		stringstream ss(line);
		if (line[0] == 'L'){
            for (size_t i = 0; i != installed.size(); ++i)
                cout << "   " << name[installed[i]] << endl;
		}
		else{
            string t1, t2, t3;
			ss >> t1 >> t2;
			if (t1[0] == 'D'){
				while (ss >> t3){
					depend[get_id(t2)].push_back(get_id(t3));
					depend2[get_id(t3)].push_back(get_id(t2));
				}
			}
			else if (t1[0] == 'I')
				instal(get_id(t2), true);
			else if (t1[0] == 'R')
				Remove(get_id(t2), true);
		}
	}
	cout << "END" << endl;
	return 0;
}