最小路径覆盖数=顶点数-最大匹配数;找路径的时候,回溯找;#include#include#include#include#include#include#include#include#include#include#include#include#include#include#include#include#include//#include//#pragma GCC optimize(2)using namespace std;#define maxn 200005#define inf 0x7fffffff//#define INF 1e18#define rdint(x) scanf("%d",&x)#define rdllt(x) scanf("%lld",&x)#define rdult(x) scanf("%lu",&x)#define rdlf(x) scanf("%lf",&x)#define rdstr(x) scanf("%s",x)typedef long long ll;typedef unsigned long long ull;typedef unsigned int U;#define ms(x) memset((x),0,sizeof(x))const long long int mod = 1e9;#define Mod 1000000000#define sq(x) (x)*(x)#define eps 1e-5typedef pair pii;#define pi acos(-1.0)//const int N = 1005;#define REP(i,n) for(int i=0;i<(n);i++)typedef pair pii;inline int rd() { int x = 0; char c = getchar(); bool f = false; while (!isdigit(c)) { if (c == '-') f = true; c = getchar(); } while (isdigit(c)) { x = (x << 1) + (x << 3) + (c ^ 48); c = getchar(); } return f ? -x : x;}ll gcd(ll a, ll b) { return b == 0 ? a : gcd(b, a%b);}int sqr(int x) { return x * x; }/*ll ans;ll exgcd(ll a, ll b, ll &x, ll &y) { if (!b) { x = 1; y = 0; return a; } ans = exgcd(b, a%b, x, y); ll t = x; x = y; y = t - a / b * y; return ans;}*/int n, m;int st, ed;int fa[maxn];void init() { for (int i = 0; i <= 2 * n + 2; i++)fa[i] = i;}struct node { int u, v, nxt, w;}edge[maxn << 1];int head[maxn], cnt;void addedge(int u, int v, int w) { edge[cnt].u = u; edge[cnt].v = v; edge[cnt].nxt = head[u]; edge[cnt].w = w; head[u] = cnt++;}int rk[maxn];int bfs() { queueq; ms(rk); rk[st] = 1; q.push(st); while (!q.empty()) { int tmp = q.front(); q.pop(); for (int i = head[tmp]; i != -1; i = edge[i].nxt) { int to = edge[i].v; if (rk[to] || edge[i].w <= 0)continue; rk[to] = rk[tmp] + 1; q.push(to); } } return rk[ed];}int dfs(int u, int flow) { if (u == ed)return flow; int add = 0; for (int i = head[u]; i != -1 && add < flow; i = edge[i].nxt) { int v = edge[i].v; if (rk[v] != rk[u] + 1 || !edge[i].w)continue; int tmpadd = dfs(v, min(edge[i].w, flow - add)); if (!tmpadd) { rk[v] = -1; continue; } edge[i].w -= tmpadd; edge[i ^ 1].w += tmpadd; add += tmpadd; } return add;}int ans;void dinic() { while (bfs())ans += dfs(st, inf);}int findfa(int x) { if (x == fa[x]) { return x; } return fa[x] = findfa(fa[x]);}int vis[maxn];void output(int x) { printf("%d ", x); for (int i = head[x]; i != -1; i = edge[i].nxt) { if (edge[i].w == 0 && edge[i].v > n)output(edge[i].v - n); }}int main(){ //ios::sync_with_stdio(0); memset(head, -1, sizeof(head)); n = rd(); m = rd(); st = 0; ed = 2 * n + 1;init(); for (int i = 1; i <= m; i++) { int u, v; u = rd(); v = rd(); addedge(u, v + n, 1); addedge(v + n, u, 0); } for (int i = 1; i <= n; i++) { addedge(st, i, 1); addedge(i, st, 0); } for (int i = 1; i <= n; i++) { addedge(i + n, ed, 1); addedge(ed, i + n, 0); } dinic(); for (int i = 0; i < cnt; i++) { if (edge[i].u >= 1 && edge[i].u <= n && edge[i].v > n&& edge[i].w == 0) { fa[findfa(edge[i].v - n)] = findfa(edge[i].u); } } for (int i = 1; i <= n; i++) { if (findfa(i) == i) { output(i); printf("\n"); } } cout << n-ans << endl; return 0;} EPFL - Fighting