UVa 753 - A Plug for UNIX（最大流 | EK）

题意

一个宾馆里有N种插座，现在有K个设备，每个设备有各自的插座类型。

还有一些转换器，提供插座类型之间的转换。

问最少剩下多少设备不能用。

思路

可以想到是最大流问题。

建一个源点，到每个插座的容量为1.

建一个汇点，到每个设备的容量为1.

插座到设备的容量为1.

转换器到插座的容量为INF。

然后跑一遍最大流吧。

代码

  
  
  
  

   
   
   
   
#include <cstdio>
   
   
   
   
#include <stack>
   
   
   
   
#include <set>
   
   
   
   
#include <iostream>
   
   
   
   
#include <string>
   
   
   
   
#include <vector>
   
   
   
   
#include <queue>
   
   
   
   
#include <functional>
   
   
   
   
#include <cstring>
   
   
   
   
#include <algorithm>
   
   
   
   
#include <cctype>
   
   
   
   
#include <ctime>
   
   
   
   
#include <cstdlib>
   
   
   
   
#include <fstream>
   
   
   
   
#include <string>
   
   
   
   
#include <sstream>
   
   
   
   
#include <map>
   
   
   
   
#include <cmath>
   
   
   
   
#define LL long long
   
   
   
   
#define SZ(x) (int)x.size()
   
   
   
   
#define Lowbit(x) ((x) & (-x))
   
   
   
   
#define MP(a, b) make_pair(a, b)
   
   
   
   
#define MS(arr, num) memset(arr, num, sizeof(arr))
   
   
   
   
#define PB push_back
   
   
   
   
#define F first
   
   
   
   
#define S second
   
   
   
   
#define ROP freopen("input.txt", "r", stdin);
   
   
   
   
#define MID(a, b) (a + ((b - a) >> 1))
   
   
   
   
#define LC rt << 1, l, mid
   
   
   
   
#define RC rt << 1|1, mid + 1, r
   
   
   
   
#define LRT rt << 1
   
   
   
   
#define RRT rt << 1|1
   
   
   
   
#define BitCount(x) __builtin_popcount(x)
   
   
   
   
const double PI = acos(-1.0);
   
   
   
   
const int INF = 0x3f3f3f3f;
   
   
   
   
using namespace std;
   
   
   
   
const int MAXN = 300 + 10;
   
   
   
   
const int MOD = 20071027;
   
   
   
   

   
   
   
   
typedef pair<int, int> pii;
   
   
   
   
typedef vector<int>::iterator viti;
   
   
   
   
typedef vector<pii>::iterator vitii;
   
   
   
   

   
   
   
   
map<string, int> mp;
   
   
   
   

   
   
   
   
struct EDGE
   
   
   
   
{
   
   
   
   
 int from, to, cap, flow;
   
   
   
   
};
   
   
   
   

   
   
   
   
struct MAXFLOW
   
   
   
   
{
   
   
   
   
 int N;
   
   
   
   
 int a[MAXN], p[MAXN];
   
   
   
   
 vector<EDGE> edges;
   
   
   
   
 vector<int> G[MAXN];
   
   
   
   

   
   
   
   
 void init(int N)
   
   
   
   
 {
   
   
   
   
 for (int i = 0; i < N; i++) G[i].clear();
   
   
   
   
 edges.clear();
   
   
   
   
 }
   
   
   
   

   
   
   
   
 void add_edge(int from, int to, int cap, int flow)
   
   
   
   
 {
   
   
   
   
 edges.PB((EDGE){from, to, cap, 0});
   
   
   
   
 edges.PB((EDGE){to, from, 0, 0});
   
   
   
   
 int m = SZ(edges);
   
   
   
   
 G[from].PB(m - 2); G[to].PB(m - 1);
   
   
   
   
 }
   
   
   
   

   
   
   
   
 void EK(int st, int ed, int &flow)
   
   
   
   
 {
   
   
   
   
 queue<int> qu;
   
   
   
   
 while (true)
   
   
   
   
 {
   
   
   
   
 MS(a, 0);
   
   
   
   
 a[st] = INF;
   
   
   
   
 qu.push(st);
   
   
   
   
 while (!qu.empty())
   
   
   
   
 {
   
   
   
   
 int u = qu.front(); qu.pop();
   
   
   
   
 for (int i = 0; i < SZ(G[u]); i++)
   
   
   
   
 {
   
   
   
   
 EDGE &e = edges[G[u][i]];
   
   
   
   
 if (!a[e.to] && e.cap > e.flow)
   
   
   
   
 {
   
   
   
   
 a[e.to] = min(a[u], e.cap - e.flow);
   
   
   
   
 p[e.to] = G[u][i];
   
   
   
   
 qu.push(e.to);
   
   
   
   
 }
   
   
   
   
 }
   
   
   
   
 }
   
   
   
   
 if (!a[ed]) break;
   
   
   
   
 int u = ed;
   
   
   
   
 while (u != st)
   
   
   
   
 {
   
   
   
   
 edges[p[u]].flow += a[ed];
   
   
   
   
 edges[p[u] ^ 1].flow -= a[ed];
   
   
   
   
 u = edges[p[u]].from;
   
   
   
   
 }
   
   
   
   
 flow += a[ed];
   
   
   
   
 }
   
   
   
   
 }
   
   
   
   
}maxFlow;
   
   
   
   

   
   
   
   
int main()
   
   
   
   
{
   
   
   
   
 //ROP;
   
   
   
   
 ios::sync_with_stdio(0);
   
   
   
   

   
   
   
   
 int T, i, j, n, m;
   
   
   
   
 cin >> T;
   
   
   
   
 while (T--)
   
   
   
   
 {
   
   
   
   
 int cnt = 2;
   
   
   
   
 mp.clear();
   
   
   
   
 maxFlow.init(MAXN);
   
   
   
   
 cin >> n;
   
   
   
   
 for (i = 0; i < n; i++)
   
   
   
   
 {
   
   
   
   
 string str;
   
   
   
   
 cin >> str;
   
   
   
   
 mp[str] = cnt++;
   
   
   
   
 maxFlow.add_edge(0, mp[str], 1, 0);
   
   
   
   
 }
   
   
   
   
 cin >> m;
   
   
   
   
 for (i = 1; i <= m; i++)
   
   
   
   
 {
   
   
   
   
 string thg, str;
   
   
   
   
 cin >> thg >> str;
   
   
   
   
 if (!mp.count(str))
   
   
   
   
 mp[str] = cnt++;
   
   
   
   
 mp[thg] = cnt++;
   
   
   
   
 maxFlow.add_edge(mp[str], mp[thg], 1, 0);
   
   
   
   
 maxFlow.add_edge(mp[thg], 1, 1, 0);
   
   
   
   
 }
   
   
   
   
 cin >> n;
   
   
   
   
 for (i = 0; i < n; i++)
   
   
   
   
 {
   
   
   
   
 string a, b;
   
   
   
   
 cin >> a >> b;
   
   
   
   
 if (!mp.count(a)) mp[a] = cnt++;
   
   
   
   
 if (!mp.count(b)) mp[b] = cnt++;
   
   
   
   
 maxFlow.add_edge(mp[b], mp[a], INF, 0);
   
   
   
   
 }
   
   
   
   
 int flow = 0;
   
   
   
   
 maxFlow.EK(0, 1, flow);
   
   
   
   
 printf("%d\n", m - flow);
   
   
   
   
 if (T) puts("");
   
   
   
   
 }
   
   
   
   
 return 0;
   
   
   
   
}