Dinic 算法

#include <bits/stdc++.h>
using namespace std;

const int N (1e5+5), M(1e5+5);

int head
;
struct Edge{
/*
r: residual capacity
*/
int v, r, nt;
}E[M];
int tail;
void add_edge(int u, int v, int c){
E[tail]={v, c, head[u]}, head[u]=tail++;
E[tail]={u, 0, head[v]}, head[v]=tail++;
}

int level
;
void bfs(int s){
memset(level, -1, sizeof(level));
queue<int> que;
level[s]=0;
que.push(s);
for(int u; !que.empty(); ){
u=que.front(), que.pop();
for(int i=head[u]; ~i; i=E[i].nt){
int &v=E[i].v;
if(E[i].r>0 && level[v]<0){
level[v]=level[u]+1;
que.push(v);
}
}
}
}

int iter
;
int dfs(int u, int t, int f){
/*
t: terminal (sink)
*/
if(u==t) return f;
//for(int &i=iter[u]; i!=-1; i++){
for(int &i=iter[u]; i!=-1; i=E[i].nt){
int &v=E[i].v, &r=E[i].r;
if(r>0 && level[u]<level[v]){
int d=dfs(v, t, min(f, r));
if(d>0){
r-=d;
E[i^1].r+=d;
return d;
}
}
}
return 0;
}

int dinic(int s, int t){
const int INF=1<<30;
for(int flow=0;;){
bfs(s);
if(level[t]<0) return flow;
memcpy(iter, head, sizeof(iter));
for(int f; f=dfs(s, t, INF); flow+=f);
}
}

void init(){
tail=0;
memset(head, -1, sizeof(head));
}