@[ycw123](/user/226844) AC代码
```
#include<bits/stdc++.h>
#define ll long long
#define INF 0x3f3f3f3f
using namespace std;
const int N = 1e5 + 10;
int n, m, s, t, h[N], cnt, dep[N], cur[N], to[N], tag[N];
struct node {
int v, w, nt;
} no[N];
void add(int u, int v, int w) {
no[cnt] = node{v, w, h[u]};
h[u] = cnt++;
}
int bfs() {
queue<int> q;
memset(dep, 0, sizeof dep);
dep[s] = 1;
q.push(s);
while(!q.empty()) {
int u = q.front();
q.pop();
for(int i = h[u]; ~i; i = no[i].nt) {
int v = no[i].v;
if(!dep[v] && no[i].w > 0) {
dep[v] = dep[u] + 1;
q.push(v);
}
}
}
return dep[t] > 0;
}
int dfs(int u, int flow) {
if(u == t)
return flow;
for(int i = cur[u]; ~i; i = no[i].nt) {
int v = no[i].v;
if(dep[v] == dep[u] + 1 && no[i].w > 0) {
int res = dfs(v, min(flow, no[i].w));
if(res > 0) {
no[i].w -= res;
no[i ^ 1].w += res;
if(u != s && v != t)
to[u] = v;//记录路径
if(u != s)//记录本节点非路径的根节点
tag[v - n] = 1;
return res;
}
}
}
return 0;
}
int dinic() {
int res = 0;
while(bfs()) {
for(int i = 0; i <= cnt; i++)
cur[i] = h[i];
while(int d = dfs(s, INF))
res += d;
}
for(int i = 1; i <= n; i++) {
if(!tag[i]) {
int u = i;
printf("%d ", u);
while(to[u] && to[u] != t) {
printf("%d ", to[u] - n);
u = to[u] - n;
}
puts("");
}
}
return res;
}
int main() {
//freopen("1.in", "r", stdin);
memset(h, -1, sizeof h);
scanf("%d%d", &n, &m);
t = 2 * n + 1;
for(int i = 1; i <= n; i++) {
add(s, i, 1), add(i, s, 0);
add(i + n, t, 1), add(t, i + n, 0);
}
for(int u, v, i = 1; i <= m; i++) {
scanf("%d%d", &u, &v);
add(u, v + n, 1), add(n + v, u, 0);
}
printf("%d\n", n - dinic());
return 0;
}
by WANG_ZHENG_MING @ 2022-08-03 10:43:38
找到问题了，dfs没有`return 0;`
by ycw123 @ 2022-08-22 09:09:08