递归邻接表
#include <iostream>
#include <string.h>
#include <queue>
using namespace std;
const int INF = 0x3f3f3f3f;
const int MAX_N=100; //顶点数上限
const int MAX_M=10000; //总的边数上限
struct edge{
int v,c,next; //v指另一个顶点,c表示容量。
}e[MAX_M];
int p[MAX_N],eid;
void init(){
memset(p,-1,sizeof(p));
eid=0;
}
void insert(int u,int v,int c){ //插入一条从u向v,容量为c的弧。
e[eid].v=v;
e[eid].next=p[u];
e[eid].c=c;
p[u]=eid++;
}
void addedge(int u,int v,int c){ //用insert插入网络中的弧
insert(u,v,c);
insert(v,u,0); //插入一条反方向,当前容量为0的弧
}
int S,T; //S是源点,T是汇点。
int d[MAX_N]; //存储每个顶点的层次
bool bfs(){
memset(d,-1,sizeof(d));
queue<int> q;
q.push(S);
d[S]=0;
while(!q.empty()){
int u=q.front();
q.pop();
for(int i=p[u];i!=-1;i=e[i].next){
int v=e[i].v;
if(e[i].c>0&&d[v]==-1){
q.push(v);
d[v]=d[u]+1;
}
}
}
return (d[T]!=-1);
}
int dfs(int u,int flow){ //flow表示当前搜索分支的流量上限
if(u==T){
return flow;
}
int res=0;
for(int i=p[u];i!=-1;i=e[i].next){
int v=e[i].v;
if(e[i].c>0&&d[u]+1==d[v]){
int tmp=dfs(v,min(flow,e[i].c)); // 递归计算顶点 v,用 c(u, v) 来更新当前流量上限
flow-=tmp;
e[i].c-=tmp;
res+=tmp;
e[i^1].c+=tmp; // 修改反向弧的容量
if(flow==0){ // 流量达到上限,不必继续搜索了
break;
}
}
}
if(res==0){ // 当前没有经过顶点 u 的可行流,不再搜索顶点 u
d[u]=-1;
}
return res;
}
int dinic(){ // 函数返回值就是最大流的结果
int res=0;
while(bfs()){
res+=dfs(S,INF); // 初始流量上限为 INF
}
return res;
}
int main() {
int n,m;
init();
cin>>m>>n;
for(int i=0;i<m;i++){
int u,v,flow;
cin>>u>>v>>flow;
addedge(u,v,flow);
}
cin>>S>>T;
cout<<dinic()<<endl;
return 0;
}
递归邻接矩阵
#include <iostream>
#include <string.h>
#include <queue>
using namespace std;
#define INF 0x3f3f3f3f
#define N 110
int e[N][N];
int S,T;
int n,np,nc,m;
int d[N];
bool bfs(){
memset(d,-1,sizeof(d));
queue<int> q;
q.push(S);
d[S]=0;
while(!q.empty()){
int u=q.front();
q.pop();
for(int i=0;i<n;i++){
if(e[u][i]&&d[i]==-1){
d[i]=d[u]+1;
q.push(i);
}
}
}
return d[T]!=-1;
}
int dfs(int u,int flow){
if(u==T){
return flow;
}
int res=0;
for(int i=0;i<n;i++){
if(e[u][i]&&d[i]==d[u]+1){
int tmp=dfs(i,min(flow,e[u][i]));
flow-=tmp;
e[u][i]-=tmp;
res+=tmp;
e[i][u]+=tmp;
if(flow==0) break;
}
}
if(res==0) d[u]=-1;
return res;
}
int dinic(){
int res=0;
while(bfs()){
res+=dfs(S,INF);
}
return res;
}
//#define debug
int main(){
#ifdef debug
freopen("in.txt","r",stdin);
// freopen("out.txt","w",stdout);
#endif // debug
int x,y,z;
char s[10];
while(scanf("%d%d",&n,&m)!=EOF){
while(m--){
scanf("%d%d%d",&x,&y,&z);
if(x==y) continue;
e[x][y]+=z;
}
scanf("%d%d",&S,&T);
printf("%d\n",dinic());
}
return 0;
}
非递归
#include <iostream>
#include <string.h>
#include <queue>
using namespace std;
const int INF = 0x3f3f3f3f;
const int MAX_N=205; //顶点数上限
const int MAX_M=1000; //总的边数上限
struct Edge{
int v,f,next; //v指另一个顶点,c表示容量。
}edge[MAX_M];
int first[MAX_N],eid;
void init(){
memset(first,-1,sizeof(first));
eid=0;
}
void insert(int u,int v,int c){ //插入一条从u向v,容量为c的弧。
edge[eid].v=v;
edge[eid].next=first[u];
edge[eid].f=c;
first[u]=eid++;
}
void addedge(int u,int v,int c){ //用insert插入网络中的弧
insert(u,v,c);
insert(v,u,0); //插入一条反方向,当前容量为0的弧
}
int level[MAX_N]; //存储每个顶点的层次
int q[MAX_M];
int bfs(int s, int t) //构建层次网络
{
memset(level, 0, sizeof(level));
level[s] = 1;
int front = 0, rear = 1;
q[front] = s;
while(front < rear)
{
int x = q[front++];
if(x == t) return 1;
for(int e = first[x]; e != -1; e = edge[e].next)
{
int v = edge[e].v, f = edge[e].f;
if(!level[v] && f)
{
level[v] = level[x] + 1;
q[rear++] = v;
}
}
}
return 0;
}
int Dinic(int s, int t){
int ans = 0;
while(bfs(s, t)){
int e, x, y, back, iter = 1;
while(iter){
x = (iter==1)?s:edge[q[iter-1]].v;
if (x == t){
int minCap = INF;
for (int i = 1; i < iter; i++){
e = q[i];
if (edge[e].f < minCap){
minCap = edge[e].f;
back = i;
}
}
for (int i = 1; i < iter; i++){
e = q[i];
edge[e].f -= minCap;
edge[e^1].f += minCap;
}
ans += minCap;
iter = back;
}else{
for (e = first[x]; e != -1; e = edge[e].next){
y = edge[e].v;
if (edge[e].f && level[y] == level[x]+1){
break;
}
}
if (e != -1){
q[iter++] = e;
}
else{
level[x] = -1;
iter--;
}
}
}
}
return ans;
}
int main() {
int n,m;
while(cin>>m>>n){
init();
for(int i=0;i<m;i++){
int u,v,flow;
cin>>u>>v>>flow;
addedge(u,v,flow);
}
cout<<Dinic(1,n)<<endl;
}
return 0;
}