[网络流24题]P2763 试题库

显然的建图和输出方案
https://www.luogu.com.cn/problem/P2763

点击查看代码

#include <bits/stdc++.h>
using namespace std;
#define endl '\n'
typedef long long ll;
const int INF = 0x3f3f3f3f;
const int N = 2e3 + 5;
const int M = N * N + 5;
struct edge {
    int v, w, to;
} e[M * 2];
int pre[N], cnt_edge, dep[N];
int S, T, z, head[N], sum;
int n, m, q[N], cur[N];
void add(int u, int v, int w) {
    // cout<<"add: "<<u<<" "<<v<<endl;
    e[cnt_edge] = {v, w, head[u]};
    head[u] = cnt_edge++;
    e[cnt_edge] = {u, 0, head[v]};
    head[v] = cnt_edge++;
}
bool bfs() {
    for (int i = 0; i <= T; i++) dep[i] = 0;
    dep[S] = 1;
    int l = 0, r = 1;
    q[r] = S;
    while (l < r) {
        int u = q[++l];
        for (int i = head[u]; ~i; i = e[i].to) {
            int v = e[i].v;
            if (!dep[v] && e[i].w) dep[v] = dep[u] + 1, q[++r] = v;
        }
    }
    // cout<<dep[T]<<endl;
    return dep[T];
}
int dfs(int u, int mi) {
    int res = 0;
    if (mi == 0 || u == T) return mi;
    for (int& i = cur[u]; ~i; i = e[i].to) {
        int v = e[i].v;
        if (dep[u] + 1 == dep[v] && e[i].w) {
            int minn = dfs(v, min(mi - res, e[i].w));
            e[i].w -= minn;
            e[i ^ 1].w += minn;
            res += minn;
            if (res == mi) return res;
        }
    }
    if (res == 0) dep[u] = 0;
    return res;
}
int dinic() {
    int res = 0;
    while (bfs()) {
        memcpy(cur, head, sizeof head);
        res += dfs(S, INF);
    }
    return res;
}
int k;
int id(int x, int on) { return on * n + x; }
int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    memset(head, -1, sizeof head);
    cin >> k >> n;
    S = n + k + 1, T = S + 1;
    int val;
    int sum = 0;
    for (int i = 1; i <= k; i++) {
        cin >> val;
        add(id(i, 1), T, val);
        sum += val;
    }
    int cnt = 0;
    for (int i = 1; i <= n; i++) {
        cin >> cnt;
        for (int j = 0, v; j < cnt; j++) {
            cin >> v;
            add(id(i, 0), id(v, 1), 1);
        }
        add(S, id(i, 0), 1);
    }
    int ans = dinic();
    // cout << ans << endl;
    if (ans == sum) {
        for (int i = 1; i <= k; i++) {
            cout << i << ":";
            for (int j = head[i + n]; ~j; j = e[j].to) {
                int v = e[j].v;
                // cout<<" "<<v<<" "<<e[j^1].w<<endl; + n
                if (e[j ^ 1].w == 0 && v != T) {
                    cout << " " << v;
                    // e[j].w--;
                    // e[j^ 1 ].w++;
                }
            }
            cout << endl;
        }
    } else {
        cout << "No Solution!";
    }
}