POJ 1087 —— A Plug for UNIX

原题：http://poj.org/problem?id=1087

题意：n个插座，m个电器及其对应的插座，k种转化器，转换器（u，v）表示可以把原本需要u插座的电器转接到v插座上，问最少有多少设备没有插座用，每种转换器数量不限;；

#include<cstdio>
#include<cstring>
#include<string>
#include<queue>
#include<vector>
#include<map>
#include<algorithm>
#define inf 1e9
using namespace std;
const int maxn = 1500;
const int maxm = 5500;
int n, m, k;
int num_nodes;
int a[30];
map<string, int>mp;

struct Edge
{
    int from, to, flow, cap;
}edge[maxm*2];  

vector<int>G[maxn];
int edgenum;
void add(int u, int v, int c)
{
    edge[edgenum].from = u;
    edge[edgenum].to = v;
    edge[edgenum].flow = 0;
    edge[edgenum].cap = c;
    edgenum++;  

    edge[edgenum].from = v;
    edge[edgenum].to = u;
    edge[edgenum].flow = 0;
    edge[edgenum].cap = 0;
    edgenum++;  

    G[u].push_back(edgenum-2);
    G[v].push_back(edgenum-1);
}  

int deep[maxn];
bool vis[maxn];
void BFS(int s, int t)
{
    queue<int>Q;
    memset(vis, false, sizeof vis);
    Q.push(t);
    vis[t] = true;
    deep[t] = 0;
    while(!Q.empty())
    {
        int now = Q.front();
        Q.pop();
        for(int i = 0;i<(int)G[now].size();i++)
        {
            int v = edge[G[now][i]].to;
            if(!vis[v])
			{
                deep[v] = deep[now] + 1;
                vis[v] = true;
                Q.push(v);
            }
        }
    }
}  

int gap[maxn];
int cur[maxn];
int front[maxn];
int Augment(int s, int t)
{
    int minflow = inf;
    int begin = t;
    while(begin != s)
    {
        Edge& e = edge[front[begin]];
        minflow = min(minflow, e.cap - e.flow);
        begin = e.from;
    }  

    begin = t;
    while(begin != s)
    {
        edge[front[begin]].flow += minflow;
        edge[front[begin]^1].flow -= minflow;
        begin = edge[front[begin]].from;
    }
    return minflow;
}  

int Maxflow(int s, int t)
{
    int flow = 0;
    BFS(s, t);
    memset(gap, 0, sizeof gap);
    memset(cur, 0, sizeof cur);
    for(int i = 0;i<num_nodes;i++)  gap[deep[i]]++;
    int begin = s;
    while(deep[s] < num_nodes)
    {
        if(begin == t)
		{
            flow += Augment(s, t);
            begin = s;
        }
        bool flag = false;
        for(int i = cur[begin];i<(int)G[begin].size();i++)
        {
            Edge& e = edge[G[begin][i]];
            if(e.cap > e.flow && deep[begin] == deep[e.to] + 1)
			{
                front[e.to] = G[begin][i];
                cur[begin] = i;
                flag = true;
                begin = e.to;
                break;
            }
        }
        if(!flag)
        {
            int k = num_nodes-1;
            for(int i = 0;i<(int)G[begin].size();i++)
			{
                Edge& e = edge[G[begin][i]];
                if(e.cap > e.flow)
                    k = min(k, deep[e.to]);
            }
            if(--gap[deep[begin]] == 0) break;
            gap[deep[begin] = k+1]++;
            cur[begin] = 0;
            if(begin != s)
                begin = edge[front[begin]].from;
        }
    }
    return flow;
}  

void init()
{
    for(int i = 0;i<num_nodes+2;i++) G[i].clear();
    edgenum = 0;
    memset(deep, 0, sizeof deep);
}

int cnt = 0;
int Id(char s[])
{
	if(mp.find(s) == mp.end())
		mp[s] = ++cnt;
	return mp[s];
}

int main()
{
	int s = 0, t = 400;
	num_nodes = t+1;
	init();
	scanf("%d", &n);
	char c[5];
	mp.clear();
	for(int i = 1;i<=n;i++)
	{
		scanf("%s", c);
		add(Id(c), t, 1);
	}
	scanf("%d", &m);
	char thing[30];
	for(int i = 1;i<=m;i++)
	{
		scanf("%s%s", thing, c);
		add(s, i+n, 1);
		add(i+n, Id(c), 1);
	}
	scanf("%d", &k);
	char u[5], v[5];
	for(int i = 1;i<=k;i++)
	{

		scanf("%s%s", u, v);
		add(Id(u), Id(v), inf);
	}
	int flow = Maxflow(s, t);
	printf("%d\n", m-flow);
	return 0;
}