上面那个链接放错了，重新放一下：[我的提交记录](https://www.luogu.com.cn/record/106258027)
代码：
```cpp
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const ll maxn = 400, maxm = 20000;
const ll N = maxn * 2 + 10, M = maxm + 10;
const ll INF = 0x3f3f3f3f3f3f3fll;
ll n, m, num, s, t, S, ans, H[N], C[N], de[N], gp[N];
bool fl;
struct edg{
ll t, nxt, len;
}E[M * 2];
void add_edg(ll x, ll y, ll w) {
++num;
E[num].t = y;
E[num].nxt = H[x];
E[num].len = w;
H[x] = num;
}
void add_edges(ll x, ll y, ll w) {
add_edg(x, y, w);
add_edg(y, x, 0);
}
ll dfs(ll x, ll y) {
if (x == t) {
return y;
}
ll z = y, res = 0;
for (ll i = C[x]; i > 0 && z > 0; i = E[i].nxt) {
C[x] = i;
ll v = E[i].t, w = E[i].len;
if (w > 0 && de[v] + 1 == de[x]) {
ll k = dfs(v, min(w, z));
E[i].len -= k;
E[(i ^ 1)].len += k;
z -= k;
res += k;
if (z == 0) {
return res;
}
}
}
--gp[de[x]];
if (gp[de[x]] == 0) {
fl = 0;
}
ll p = S;
for (ll i = H[x]; i > 0; i = E[i].nxt) {
ll v = E[i].t, w = E[i].len;
if (w > 0) {
p = min(p, de[v]);
}
}
de[x] = p + 1;
++gp[de[x]];
return res;
}
void bfs() {
for (ll i = 1; i <= S; ++i) {
de[i] = -1;
}
de[t] = 0;
for (ll i = 1; i <= S; ++i) {
gp[i] = 0;
}
queue<ll> q;
q.push(t);
while (!q.empty()) {
ll x = q.front();
q.pop();
++gp[de[x]];
for (ll i = H[x]; i > 0; i = E[i].nxt) {
ll v = E[i].t;
if (i % 2 == 1 && de[v] == -1) {
de[v] = de[x] + 1;
q.push(v);
}
}
}
}
void ISAP() {
bfs();
fl = 1;
while (de[s] < S && fl) {
for (ll i = 1; i <= S; ++i) {
C[i] = H[i];
}
fl = 1;
ll k = dfs(s, INF);
ans += k;
}
}
int main() {
scanf("%lld%lld%lld%lld", &n, &m, &s, &t);
num = 1;
S = n;
for (ll i = 1; i <= m; ++i) {
ll u, v, w;
scanf("%lld%lld%lld", &u, &v, &w);
add_edges(u, v, w);
}
ISAP();
printf("%lld", ans);
return 0;
}
```
by panhongxuanyyds @ 2023-03-29 22:22:51
@[dottle](/user/79067)
by liaoyanxu @ 2023-03-29 22:26:23
又发现了一组 hack：
$\texttt{input:}$
```
8 9 6 7
6 1 2
1 3 2
3 8 2
8 7 2
1 2 2147483647
2 7 1
6 4 1
4 5 1
5 2 1
```
$\texttt{output:}$
```
3
```
$\texttt{wrong output:}$
```
2
```
by panhongxuanyyds @ 2023-03-31 21:51:35
太棒了！找到原因了！
by duckya @ 2024-01-11 17:26:08