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| #include <bits/stdc++.h>
#define R register
#define ll long long
#define cmax(a, b) ((a < b) ? b : a)
#define cmin(a, b) ((a < b) ? a : b)
#define sum(a, b, mod) ((a + b) % mod)
const int MaxN = 2e4 + 10;
const int MaxM = 5e5 + 10;
const int inf = (1 << 30);
struct edge
{
int to, next, cap;
};
edge e[MaxM];
int n, m, s = 20000, t = 20001, cnt = 1, ans;
int head[MaxN], dep[MaxN], cur[MaxN], a[MaxN];
inline void add(int u, int v, int c)
{
++cnt;
e[cnt].to = v;
e[cnt].next = head[u];
e[cnt].cap = c;
head[u] = cnt;
}
inline void add_edge(int u, int v, int c) { add(u, v, c), add(v, u, 0); }
inline int read()
{
int x = 0;
char ch = getchar();
while (ch > '9' || ch < '0')
ch = getchar();
while (ch <= '9' && ch >= '0')
x = (x << 1) + (x << 3) + (ch ^ 48), ch = getchar();
return x;
}
inline int bfs()
{
memset(dep, 0, sizeof(dep));
memcpy(cur, head, sizeof(head));
std::queue<int> q;
dep[s] = 1;
q.push(s);
while (!q.empty())
{
int u = q.front();
q.pop();
for (int i = head[u]; i; i = e[i].next)
{
int v = e[i].to, c = e[i].cap;
if (dep[v] || !c)
continue;
dep[v] = dep[u] + 1;
q.push(v);
}
}
return dep[t];
}
inline int dinic(int u, int flow)
{
if (u == t)
return flow;
int rest = flow;
for (int i = cur[u]; i && (flow - rest < flow); i = e[i].next)
{
int v = e[i].to, c = e[i].cap;
if (dep[v] != dep[u] + 1 || !c)
continue;
int k = dinic(v, cmin(rest, c));
if (!k)
dep[v] = dep[u] + 1;
else
{
e[i].cap -= k;
e[i ^ 1].cap += k;
rest -= k;
}
}
if (flow - rest < flow)
dep[u] = -1;
return flow - rest;
}
int main()
{
n = read(), m = read();
int u, v;
for (int i = 1; i <= m; i++)
add_edge(s, i, 1);
for (int i = m + 1; i <= n; i++)
add_edge(i, t, 1);
while (scanf("%d%d", &u, &v) == 2)
add_edge(u, v, 1);
int now = 0;
while (bfs())
while ((now = dinic(s, inf)))
ans += now;
printf("%d\n", ans);
return 0;
}
|