A Plug for UNIX UVA - 753（网络流）

题意：n个插座，m个设备及其插头类型，k种转换器，没有转换器的情况下插头只能插到类型名称相同的插座中，问最少剩几个不匹配的设备

lrj紫书里面讲得挺好的。

先跑一遍floyd，看看插头类型a能否转换为b

然后构造网络

源点为0， 汇点为n + m + 1，源点连插头 容量为1，插座连汇点，容量为1

插头和插座能互相转换的容量为INF，跑一遍最大流 m - 最大流就是答案

顺便粘一下dinic的板子

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

inline int read() {
    int x = 0, f = 1; char ch = getchar();
    while (ch < ‘0‘ || ch > ‘9‘) { if (ch == ‘-‘) f = -1; ch = getchar();}
    while (ch >= ‘0‘ && ch <= ‘9‘) { x = x * 10 + ch - 48; ch = getchar();}
    return x * f;
}

const int N = 500;
const int INF = 0x3f3f3f3f;
int n, m, k, tol, cnt;
map<string, int> mp;
vector<int> a;
vector<int> b;
bool f[N][N];
struct Edge { int v, f, next; } edge[N * 2];
int head[N], level[N], iter[N];

inline void init() {
    mp.clear();
    a.clear();
    b.clear();
    tol = cnt = 0;
    memset(f, 0, sizeof(f));
    memset(head, -1, sizeof(head));
}

inline void addedge(int u, int v, int f) {
    edge[cnt].v = v; edge[cnt].next = head[u]; edge[cnt].f = f; head[u] = cnt++;
}

void floyd() {
    for (int k = 1; k <= tol; k++) {
        for (int i = 1; i <= tol; i++) {
            for (int j = 1; j <= tol; j++) {
                f[i][j] = f[i][j] || (f[i][k] && f[k][j]);
            }
        }
    }
}

bool bfs(int s, int t) {
    for (int i = 0; i <= t; i++) iter[i] = head[i], level[i] = -1;
    level[s] = 0;
    queue<int> que;
    que.push(s);
    while (!que.empty()) {
        int u = que.front(); que.pop();
        for (int i = head[u]; ~i; i = edge[i].next) {
            int v = edge[i].v, f = edge[i].f;
            if (f > 0 && level[v] == -1) {
                level[v] = level[u] + 1;
                que.push(v);
            }
        }
    }
    return level[t] != -1;
}

int dfs(int u, int t, int f) {
    if (!f || u == t) return f;
    int flow = 0, w;
    for (int i = iter[u]; ~i; i = edge[i].next) {
        iter[u] = i;
        int v = edge[i].v;
        if (level[v] == level[u] + 1 && edge[i].f > 0) {
            w = dfs(v, t, min(f, edge[i].f));
            if (w == 0) continue;
            f -= w;
            edge[i].f -= w;
            edge[i^1].f += w;
            flow += w;
            if (f <= 0) break;
        }
    }
    return flow;
}

int dinic(int s, int t) {
    int ans = 0;
    while (bfs(s, t)) ans += dfs(s, t, INF);
    return ans;
}

int main() {
    int T = read();
    while (T--) {
        init();
        n = read();
        for (int i = 1; i <= n; i++) {
            string s;
            cin >> s;
            mp[s] = i;
            a.emplace_back(i);
            tol++;
        }
        m = read();
        for (int i = 1; i <= m; i++) {
            string str1, s;
            cin >> str1 >> s;
            if (!mp.count(s)) {
                mp[s] = ++tol;
            }
            b.emplace_back(mp[s]);
        }
        k = read();
        for (int i = 1; i <= k; i++) {
            string s1, s2;
            cin >> s1 >> s2;
            if (!mp.count(s1)) mp[s1] = ++tol;
            if (!mp.count(s2)) mp[s2] = ++tol;
            f[mp[s1]][mp[s2]] = 1;
        }
        for (int i = 1; i <= tol; i++) f[i][i] = 1;
        floyd();
        for (int i = 1; i <= m; i++) {
            addedge(0, i, 1);
            addedge(i, 0, 0);
        }
        for (int i = 1; i <= n; i++) {
            addedge(m + i, n + m + 1, 1);
            addedge(n + m + 1, m + i, 0);
        }
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                if (!f[b[i]][a[j]]) continue;
                addedge(i + 1, m + j + 1, INF);
                addedge(m + j + 1, i + 1, 0);
            }
        }
        printf("%d\n", m - dinic(0, n + m + 1));
        if (T) puts("");
    }
    return 0;
}

原文地址：https://www.cnblogs.com/Mrzdtz220/p/10799423.html