POJ 1087--A Plug for UNIX【最大流dinic】

标签：

Description

Input

Output

Sample Input

4 
A 
B 
C 
D 
5 
laptop B 
phone C 
pager B 
clock B 
comb X 
3 
B X 
X A 
X D 

Sample Output

1

n个插座，m个电器及其对应的插座，k个转化器，前一个插座可以转化为后一个插座，问最少有多少设备没有插座用，转换器数量不限

最大流，源点向插座建边，容量为1，电器向汇点建边，容量为1，相应的插座和电器连边，容量为1，前一个插座转化为后一个插座，后一个插座向前一个插座建边，容量为无穷大，求得的最大流即为最多配对的电器。

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <iostream>
#include <queue>
#include <map>
#define maxn 10000
#define maxm 1000000
#define INF 0x3f3f3f3f
using namespace std;

int head[maxn], cur[maxn], cnt;
int dist[maxn], vis[maxn];
int n;// 插座个数
int m;// 电器个数
int k;// 转换器个数
int sect; //超级汇点
struct node{
    int u, v, cap, flow, next;
};

node edge[maxm];
map<string, int>mp;

void init(){
    cnt = 0;
    memset(head, -1, sizeof(head));
    mp.clear();
}

void add(int u, int v, int w){
    edge[cnt] = {u, v, w, 0, head[u]};
    head[u] = cnt++;
    edge[cnt] = {v, u, 0, 0, head[v]};
    head[v] = cnt++;
}

void getmap(){
    char s[30];
    char str[30];
    int ans = 1;
    while(n--){
        scanf("%s", s);
        mp[s] = ans++;
        add(0, mp[s], 1); // 0为超级源点
    }
    scanf("%d", &m);
    for(int i = 0 ; i < m; ++i){
        scanf("%s%s", str, s);
        mp[str] = ans++;
        if(!mp[s]){
            mp[s] = ans++;
        }
        add(mp[s], mp[str], 1);
        add(mp[str], sect, 1);
    }
    scanf("%d", &k);
    while(k--){
        scanf("%s%s", s, str);
        if(!mp[s])
            mp[s] = ans++;
        if(!mp[str])
            mp[str] = ans++;
        add(mp[str], mp[s], INF);//后一个插座向前一个插座建边
    }
}

bool BFS(int st, int ed){
    queue<int>q;
    memset(vis, 0, sizeof(vis));
    memset(dist, -1, sizeof(dist));
    vis[st] = 1;
    dist[st] = 0;
    q.push(st);
    while(!q.empty()){
        int u  = q.front();
        q.pop();
        for(int i = head[u]; i != -1; i = edge[i].next){
            node E = edge[i];
            if(!vis[E.v] && E.cap > E.flow){
                vis[E.v] = 1;
                dist[E.v] = dist[u] + 1;
                if(E.v == ed) return true;
                q.push(E.v);
            }
        }
    }
    return false;
}

int DFS(int x, int ed, int a){
    if(x == ed || a == 0)
        return a;
    int flow = 0, f;
    for(int &i = cur[x]; i != -1; i = edge[i].next){
        node &E = edge[i];
        if(dist[E.v] == dist[x] + 1 && (f = DFS(E.v, ed, min(a, E.cap - E.flow))) > 0){
            E.flow += f;
            edge[i ^ 1].flow -= f;
            a -= f;
            flow += f;
            if(a == 0) break;
        }
    }
    return flow;
}

int maxflow(int st, int ed){
    int flowsum = 0;
    while(BFS(st, ed)){
        memcpy(cur, head, sizeof(head));
        flowsum += DFS(st, ed, INF);
    }
    return flowsum;
}
int main(){
    while(scanf("%d", &n)!=EOF){
        sect = n + m + k + 1;
        init();
        getmap();
        int sum;
        sum = maxflow(0 , sect);
        printf("%d\n", m - sum);
    }
    return 0;
}

POJ 1087--A Plug for UNIX【最大流dinic】

标签：

原文地址：http://blog.csdn.net/hpuhjh/article/details/47315333