Dinic
#include<cstdio>
#include<iostream>
#include<cstdlib>
#include<cstring>
#include<algorithm>
#include<cmath>
#include<queue>
#define maxn 10500
#define inf 1e9
using namespace std;
int n,m,tot=1,head[maxn],S,T,t1,t2,t3;
int d[maxn],flag[maxn],cur[maxn],ans,fl[maxn];
long long anse,ansv;
struct node{
int v,nex,cap;
}e[200005];
void Q(){
tot=1;
memset(head,0,sizeof head);
}
void lj(int t1,int t2,int t3){
tot++;e[tot].v=t2,e[tot].cap=t3;e[tot].nex=head[t1];head[t1]=tot;
}
bool BFS(){
for(int i=1;i<=Max;i++)d[i]=inf,flag[i]=0;
queue<int>q;q.push(S);d[S]=0;
while(!q.empty()){
int x=q.front();q.pop();cur[x]=head[x];
for(int i=head[x];i;i=e[i].nex){
if(d[e[i].v]>d[x]+1&&e[i].cap){
d[e[i].v]=d[x]+1;
if(!flag[e[i].v]){
flag[e[i].v]=1;q.push(e[i].v);
}
}
}
flag[x]=0;
}
return d[T]!=inf;
}
int lian(int k,int a){
//cout<<k<<' '<<a<<endl;
if(k==T||!a)return a;
int f,flow=0;
for(int& i=cur[k];i;i=e[i].nex){
if(d[e[i].v]==d[k]+1&&(f=lian(e[i].v,min(a,e[i].cap)))>0){
flow+=f;a-=f;
e[i].cap-=f;e[i^1].cap+=f;
if(!a)break;
}
}
return flow;
}
int main()
{
scanf("%d%d%d%d",&n,&m,&S,&T);
for(int i=1;i<=m;i++){
scanf("%d%d%d",&t1,&t2,&t3);
lj(t1,t2,t3);lj(t2,t1,0);
}
ans=0;
while(BFS())ans+=lian(S,inf);
cout<<ans<<endl;
return 0;
}ISAP（现在不会了）
#include<cstdio>
#include<iostream>
#include<cstdlib>
#include<cstring>
#include<string>
#include<algorithm>
#include<cmath>
#include<map>
#include<queue>
#define maxn 10005
#define maxm 100005
#define inf 1e9
using namespace std;
int n,m,S,T,now[maxn],head[maxn],t1,t2,t3,tot=1;
int flag[maxn],d[maxn],pre[maxn],num[maxn],ans;
struct node
{
int nex,v,cap;
}e[maxm*2];
void lj(int t1,int t2,int t3)
{
tot++;e[tot].v=t2,e[tot].cap=t3;e[tot].nex=head[t1];head[t1]=tot;
}
void BFS(){
queue<int>q;
flag[T]=1;q.push(T);
while(!q.empty()){
int x=q.front();q.pop();
///printf("orz %d
",x);
for(int i=head[x];i;i=e[i].nex){
if(!flag[e[i].v]&&e[i^1].cap>0){
flag[e[i].v]=1;
d[e[i].v]=d[x]+1;
q.push(e[i].v);
}
}
}
}
int get()
{
int flow=inf;
for(int i=T;;i=e[pre[i]].v)
{
if(i==S)break;
flow=min(e[pre[i]^1].cap,flow);
}
for(int i=T;;i=e[pre[i]].v){
if(i==S)break;
e[pre[i]].cap+=flow;
e[pre[i]^1].cap-=flow;
}
return flow;
}
void lian()
{
BFS();
memset(num,0,sizeof(num));
//for(int i=1;i<=n;i++)cout<<d[i]<<' ';cout<<endl;
for(int i=1;i<=n;i++){now[i]=head[i];num[d[i]]++;}
int x=S;
while(d[S]<n)
{
if(x==T)ans+=get(),x=S;
bool ff=0;
for(int i=now[x];i;i=e[i].nex){
// printf("%d %d %d %d
",x,e[i].v,d[x],d[e[i].v]);
if(d[e[i].v]==d[x]-1&&e[i].cap){
ff=1;pre[e[i].v]=i^1;
now[x]=i;x=e[i].v;
break;
}
}
//printf("%d %d %d
",x,ans,ff);
if(!ff){
int mi=inf;
for(int i=head[x];i;i=e[i].nex){
if(e[i].cap>0){
//cout<<i<<' '<<d[i]<<'
';
mi=min(d[e[i].v],mi);
}
}
//cout<<endl;
num[d[x]]--;
//printf("trsae %d %d
",d[x],mi);
if(num[d[x]]==0)break;
if(mi==inf)mi=n;
d[x]=mi+1;num[d[x]]++;now[x]=head[x];
if(x!=S)x=e[pre[x]].v;
}
}
}
int main(){
cin>>n>>m>>S>>T;
for(int i=1;i<=m;i++)
{
scanf("%d%d%d",&t1,&t2,&t3);
lj(t1,t2,t3);lj(t2,t1,0);
}
lian();
printf("%d
",ans);
return 0;
}费用流（单路增广）
#include<cstdio>
#include<iostream>
#include<cstdlib>
#include<cstring>
#include<string>
#include<algorithm>
#include<cmath>
#include<map>
#include<queue>
#define maxn 5002
#define inf 1e9
using namespace std;
int n,m,S,T,head[maxn],tot=1,t1,t2,t3,t4,fl;
int d[maxn],flag[maxn],ans,cur[maxn];
struct node{
int v,nex,cap,w;
}e[100002];
void lj(int t1,int t2,int t3,int t4){
tot++;e[tot].v=t2;e[tot].cap=t3;e[tot].w=t4;e[tot].nex=head[t1];head[t1]=tot;
}
bool spfa(){
for(int i=1;i<=n;i++)d[i]=inf,flag[i]=0;
queue<int>q;q.push(S);d[S]=0;
while(!q.empty()){
int x=q.front();q.pop();
for(int i=head[x];i;i=e[i].nex){
if(e[i].cap>0&&d[e[i].v]>d[x]+e[i].w){
d[e[i].v]=d[x]+e[i].w;
if(!flag[e[i].v])flag[e[i].v]=1,q.push(e[i].v);
}
}
flag[x]=0;
}
return d[T]!=inf;
}
int dfs(int k,int a){
flag[k]=1;
if(k==T||a==0)return a;
int f,flow=0;
for(int &i=cur[k];i;i=e[i].nex){
if(d[e[i].v]==d[k]+e[i].w&&e[i].cap&&!flag[e[i].v]){//attention!!!
f=dfs(e[i].v,min(e[i].cap,a));
flow+=f;a-=f;e[i].cap-=f;e[i^1].cap+=f;
ans+=f*e[i].w;
if(a==0)break;
}
}
return flow;
}
int main(){
cin>>n>>m>>S>>T;
for(int i=1;i<=m;i++){
scanf("%d%d%d%d",&t1,&t2,&t3,&t4);
lj(t1,t2,t3,t4);lj(t2,t1,0,-t4);
}
while(spfa()){
flag[T]=1;
while(flag[T]){
memset(flag,0,sizeof(flag));
for(int i=1;i<=n;i++)cur[i]=head[i];
fl+=dfs(S,inf);
}
}
cout<<fl<<' '<<ans<<endl;
return 0;
}费用流（zkw）
#include<cstdio>
#include<iostream>
#include<cstdlib>
#include<cstring>
#include<string>
#include<algorithm>
#include<cmath>
#include<map>
#include<queue>
#define maxn 5002
#define inf 1e9
using namespace std;
int n,m,S,T,head[maxn],tot=1,t1,t2,t3,t4,fl;
int d[maxn],flag[maxn],ans,cur[maxn];
struct node{
int v,nex,cap,w;
}e[100002];
void lj(int t1,int t2,int t3,int t4){
tot++;e[tot].v=t2;e[tot].cap=t3;e[tot].w=t4;e[tot].nex=head[t1];head[t1]=tot;
}
bool spfa(){
for(int i=1;i<=n;i++)d[i]=inf,flag[i]=0;
queue<int>q;q.push(S);d[S]=0;
while(!q.empty()){
int x=q.front();q.pop();
for(int i=head[x];i;i=e[i].nex){
if(e[i].cap>0&&d[e[i].v]>d[x]+e[i].w){
d[e[i].v]=d[x]+e[i].w;
if(!flag[e[i].v])flag[e[i].v]=1,q.push(e[i].v);
}
}
flag[x]=0;
}
return d[T]!=inf;
}
int dfs(int k,int a){
flag[k]=1;
if(k==T||a==0)return a;
int f,flow=0;
for(int &i=cur[k];i;i=e[i].nex){
if(d[e[i].v]==d[k]+e[i].w&&e[i].cap&&!flag[e[i].v]){//attention!!!
f=dfs(e[i].v,min(e[i].cap,a));
flow+=f;a-=f;e[i].cap-=f;e[i^1].cap+=f;
ans+=f*e[i].w;
if(a==0)break;
}
}
return flow;
}
int main(){
cin>>n>>m>>S>>T;
for(int i=1;i<=m;i++){
scanf("%d%d%d%d",&t1,&t2,&t3,&t4);
lj(t1,t2,t3,t4);lj(t2,t1,0,-t4);
}
while(spfa()){
flag[T]=1;
while(flag[T]){
memset(flag,0,sizeof(flag));
for(int i=1;i<=n;i++)cur[i]=head[i];
fl+=dfs(S,inf);
}
}
cout<<fl<<' '<<ans<<endl;
return 0;
}