标签:cin cap 最小 == bre for 注意 最大 最小路径覆盖
最小路径覆盖=节点数-最大匹配数,拆成二分图跑dinic/匈牙利即可,注意输出路径的时候判断拆成的入点和出点和另加的反向边
#include<bits/stdc++.h> using namespace std; #define lowbit(x) ((x)&(-x)) typedef long long LL; const int maxm = 2e4+5; const int INF = 0x3f3f3f3f; struct edge{ int u, v, cap, flow, nex; } edges[maxm]; int head[maxm], cur[maxm], cnt, n, level[333]; bool vis[333]; void init() { memset(head, -1, sizeof(head)); } void add(int u, int v, int cap) { edges[cnt] = edge{u, v, cap, 0, head[u]}; head[u] = cnt++; } void addedge(int u, int v, int cap) { add(u, v, cap), add(v, u, 0); } void bfs(int s) { memset(level, -1, sizeof(level)); queue<int> q; level[s] = 0; q.push(s); while(!q.empty()) { int u = q.front(); q.pop(); for(int i = head[u]; i != -1; i = edges[i].nex) { edge& now = edges[i]; if(now.cap > now.flow && level[now.v] < 0) { level[now.v] = level[u] + 1; q.push(now.v); } } } } int dfs(int u, int t, int f) { if(u == t) return f; for(int& i = cur[u]; i != -1; i = edges[i].nex) { edge& now = edges[i]; if(now.cap > now.flow && level[u] < level[now.v]) { int d = dfs(now.v, t, min(f, now.cap - now.flow)); if(d > 0) { now.flow += d; edges[i^1].flow -= d; return d; } } } return 0; } int dinic(int s, int t) { int maxflow = 0; for(;;) { bfs(s); if(level[t] < 0) break; memcpy(cur, head, sizeof(head)); int f; while((f = dfs(s, t, INF)) > 0) maxflow += f; } return maxflow; } void print(int u, int s, int t) { if(vis[u]) return; vis[u] = true; cout << u << " "; for(int i = head[u]; i != -1; i = edges[i].nex) { auto now = edges[i]; if(now.flow && now.v != s) if(!vis[now.v-n]) print(now.v-n,s,t); } } void run_case() { init(); int m, u, v; cin >> n >> m; int s = 0, t = (n<<1)+2; for(int i = 0; i < m; ++i) { cin >> u >> v; addedge(u, v+n, 1); } for(int i = 1; i <= n; ++i) { addedge(s, i, 1); addedge(i+n, t, 1); } int ans = n - dinic(s, t); for(int i = 1; i <= n; ++i) { if(!vis[i]) { print(i,s,t); cout << "\n"; } } cout << ans; } int main() { ios::sync_with_stdio(false), cin.tie(0); run_case(); cout.flush(); return 0; }
标签:cin cap 最小 == bre for 注意 最大 最小路径覆盖
原文地址:https://www.cnblogs.com/GRedComeT/p/12298442.html