hdu 6118 最小费用可行流（注意与最大流的区别）

#include<bits/stdc++.h>
using namespace std;
#define MEM(a,b) memset(a,b,sizeof(a))
#define bug puts("bug");
#define PB push_back
#define MP make_pair
#define X first
#define Y second
typedef unsigned long long ll;
typedef pair<int,int> pii;
const int maxn=4e5+10;
const int mod=1000000007;
using namespace std;
int a[maxn],b[maxn],c[maxn],d[maxn],n,m;

const int MAXN = 10000;
const int MAXM = 100000;
const int INF = 0x3f3f3f3f;
struct Edge{
int to,next,cap,flow,cost;
} edge[MAXM];
int head[MAXN],tol;
int pre[MAXN],dis[MAXN];
bool vis[MAXN];
int N;
void init(int n){
N = n;
tol = 0;
memset(head,-1,sizeof(head));
}
void addedge(int u,int v,int cap,int cost){
edge[tol].to = v;
edge[tol].cap = cap;
edge[tol].cost = cost;
edge[tol].flow = 0;
edge[tol].next = head[u];
head[u] = tol++;
edge[tol].to = u;
edge[tol].cap = 0;
edge[tol].cost = -cost;
edge[tol].flow = 0;
edge[tol].next = head[v];
head[v] = tol++;
}
bool spfa(int s,int t){
queue<int>q;
for(int i = 0; i < N; i++){
dis[i] = INF;
vis[i] = false;
pre[i] = -1;
}
dis[s] = 0;
vis[s] = true;
q.push(s);
while(!q.empty()){
int u = q.front();
q.pop();
vis[u] = false;
for(int i = head[u]; i != -1; i = edge[i].next){
int v = edge[i].to;
if(edge[i].cap > edge[i].flow &&dis[v] > dis[u] + edge[i].cost ){
dis[v] = dis[u] + edge[i].cost;
pre[v] = i;
if(!vis[v]){
vis[v] = true;
q.push(v);
}
}
}
}
return dis[t]<=0;//可行流!!!!!!
//if(pre[t] == -1)return false;
//else return true;//最大流
}

int minCostMaxflow(int s,int t,int &cost){
int flow = 0;
cost = 0;
while(spfa(s,t)){
int Min = INF;
for(int i = pre[t]; i != -1; i = pre[edge[i^1].to]){
if(Min > edge[i].cap - edge[i].flow)
Min = edge[i].cap - edge[i].flow;
}
for(int i = pre[t]; i != -1; i = pre[edge[i^1].to]){
edge[i].flow += Min;
edge[i^1].flow -= Min;
cost += edge[i].cost * Min;
}
flow += Min;
}
return flow;
}
int main(){
while(~scanf("%d%d",&n,&m)){
init(n+3);
for(int i=1;i<=n;i++){
scanf("%d%d%d%d",&a[i],&b[i],&c[i],&d[i]);
addedge(0,i,b[i],a[i]);
addedge(i,n+1,d[i],-c[i]);
}
int x,y,z;
for(int i=1;i<=m;i++){
scanf("%d%d%d",&x,&y,&z);
addedge(x,y,1e9,z);
addedge(y,x,1e9,z);
}
int ans=0;
minCostMaxflow(0,n+1,ans);
cout<<-ans<<endl;
}
return 0;
}