LOJ 6002「网络流 24 题」最小路径覆盖

最小路径覆盖的模板题。但是我是在hihocoder上才学到这个模版的，hihocoder上面有最小路径覆盖浅显易懂的解释，非常棒！

代码如下：

#include<iostream>#include<cstdio>#include<vector>#include<queue>#include<utility>#include<stack>#include<algorithm>#include<cstring>#include<string>#include<stack>using namespace std;const int INF = 0x3f3f3f3f;const int maxn = 1000 + 10;const int maxm = 30005;int n, m;vector<int>road[205];int road_num = 0;inline int read(){int x=0,t=1,c;while(!isdigit(c=getchar()))if(c=='-')t=-1;while(isdigit(c))x=x*10+c-'0',c=getchar();return x*t;}int head[maxn],cur[maxn],nx[maxm<<1],to[maxm<<1],flow[maxm<<1],ppp=0;struct Dinic{int dis[maxn];int s, t;long long ans;void init() {memset(head, -1, sizeof(head));ppp = 0;}void AddEdge(int u, int v, int c){to[ppp]=v;flow[ppp]=c;nx[ppp]=head[u];head[u]=ppp++;swap(u,v);to[ppp]=v;flow[ppp]=0;nx[ppp]=head[u];head[u]=ppp++;}bool BFS(){memset(dis, -1, sizeof(dis));dis[s] = 1; queue<int> Q;Q.push(s);while(!Q.empty()){int x = Q.front();Q.pop();for(int i = head[x]; ~i; i = nx[i]){if(flow[i] && dis[to[i]] == -1){dis[to[i]] = dis[x] + 1;Q.push(to[i]);}}}return dis[t] != -1;}int DFS(int x, int maxflow){if(x == t || !maxflow){ans += maxflow;return maxflow;}int ret = 0, f;for(int &i = cur[x]; ~i; i = nx[i]){if(dis[to[i]] == dis[x] + 1 && (f = DFS(to[i], min(maxflow, flow[i])))){ret += f;flow[i] -= f;flow[i^1] += f;maxflow -= f;if(!maxflow)break;}}return ret;}long long solve(int source, int tank){s = source;t = tank;ans = 0;while(BFS()){memcpy(cur, head, sizeof(cur));DFS(s, INF);}return ans;}}dinic;void dfs(int x) {for(int i = head[x]; ~i; i = nx[i]) {int v = to[i];if(flow[i] == 0 && v != 0) {road[road_num].push_back(v / 2);dfs(v - 1);}}}int main() {#ifndef ONLINE_JUDGEfreopen("in.txt", "r", stdin);//freopen("out.txt", "w", stdout);#endifdinic.init();n = read(), m = read(); while(m--) {int u = read(), v = read();dinic.AddEdge(u * 2, v * 2 + 1, 1);}for(int i = 1; i <= n; i++) {dinic.AddEdge(0, i * 2, 1);dinic.AddEdge(i * 2 + 1, 1, 1);}int ans = dinic.solve(0, 1);for(int i = 1; i <= n; i++) {bool flag = 0;for(int j = head[i * 2 + 1]; ~j; j = nx[j]) {int v = to[j];if(flow[j] && to[j] == 1) {flag = 1;}}if(flag) {road[road_num].push_back(i);dfs(i * 2);road_num++;}}for(int i = 0; i < road_num; i++) {sort(road[i].begin(), road[i].end());for(int j = 0; j < road[i].size(); j++) {printf("%d%c", road[i][j], j == road[i].size() - 1 ? '\n' : ' ');}}cout << n - ans << '\n';return 0;}