你怎么学网络流了/jk
by AzusagawaKaede @ 2022-01-26 19:06:08
1. `pos[u][v] = G[u].size() - 1;`有误。当`G[u].size() - 1`的值为`0`时，对重边的判定`if(!pos[u][v])`会失效。建议将`pos`数组全初始化为`-1`，判定改为`if(pos[u][v]==-1)`。
2. `pos[u][v] = G[u].size() - 1;`还有误qwq。应将其反边`v->u`也存入`pos`，即添加一行代码`pos[v][u] = G[v].size() - 1;`。当然这个时候你就不需要`rev`了。
3. `maxn`应设为`205`,因为那些数组都是存的下标都是指结点。你设得太大会使`pos[maxn][maxn]`爆空间，在你谷下可能没事，但在`NOILinux`下会直接全`MLE`。
然后就可以`AC`了呢~
by AzusagawaKaede @ 2022-01-26 20:05:28
这是修改后的代码awa：
```
#include <iostream>
#include <cstdio>
#include <cstring>
#include <vector>
#include <queue>
#define ll long long
#define int long long
using namespace std;
const ll maxn = 205;//不算错误的错误3
const ll inf = 0x7fffffff;
struct edge{ll v,w,rev;};
ll n,m,S,T,pos[maxn][maxn],minn[maxn],pre[maxn],ans;
vector <edge> G[maxn];
bool vis[maxn];
bool bfs()
{
queue <ll> q;
q.push(S);
minn[S]= inf;
vis[S] = 1;
while(!q.empty())
{
ll tmp = q.front();
q.pop();
for(ll i = 0;i < G[tmp].size();++i)
if(G[tmp][i].w>0)
{
if(vis[G[tmp][i].v]) continue;
minn[G[tmp][i].v] = min(minn[tmp],G[tmp][i].w);
pre[G[tmp][i].v] = tmp;
q.push(G[tmp][i].v);
vis[G[tmp][i].v] = 1;
if(G[tmp][i].v==T) return 1;
}
}
return 0;
}
ll update()
{
ll x = T;
while(x != S)
{
G[pre[x]][pos[pre[x]][x]].w -= minn[T];
G[x][G[pre[x]][pos[pre[x]][x]].rev].w += minn[T];
x = pre[x];
}
return minn[T];
}
ll ek(ll s,ll t)
{
ll flow = 0;
while(1)
{
memset(vis,0,sizeof(vis));
bool f = bfs();
if(f == 0) return flow;
flow += update();
}
}
main()
{
cin >> n >> m >> S >> T;
for (int i = 1; i <= n; ++i)
for (int j = 1; j <= n; ++j)
pos[i][j] = -1;//错误1
for(ll i = 1,u,v,w;i <= m;++i)
{
scanf("%lld%lld%lld",&u,&v,&w);
if(pos[u][v] == -1)//错误1
{
G[u].push_back((edge){v,w,G[v].size()});
G[v].push_back((edge){u,0,G[u].size()-1});
pos[u][v] = G[u].size() - 1;
pos[v][u] = G[v].size() - 1;//错误2
}
else G[u][pos[u][v]].w += w;
}
printf("%lld\n",ek(S,T));
return 0;
}
```
by AzusagawaKaede @ 2022-01-26 20:10:27
谢谢zzy大佬！
我的垃圾代码我自己都看不下去，您尽然有耐心一行行看玩，调出来
（话说luogu的数据太水，这都能73
by otislee601 @ 2022-01-26 22:58:53
话说dalao最近在学什么
by otislee601 @ 2022-01-26 23:01:23