版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/a1046765624/article/details/82941696
题目描述
n nn 个点，m mm 条边，每条边 e ee 有一个流量下界 lower(e) \text{lower}(e)lower(e) 和流量上界 upper(e) \text{upper}(e)upper(e)，给定源点 s ss 与汇点 t tt，求源点到汇点的最小流。
输入格式
第一行两个正整数 n nn、m mm、s ss、t tt。
之后的 m mm 行，每行四个整数 s ss、t tt、lower \text{lower}lower、upper \text{upper}upper。
输出格式
如果无解，输出一行 please go home to sleep。
否则输出最小流。
样例
样例输入
7 12 6 7
6 1 0 2147483647
1 7 0 2147483647
6 2 0 2147483647
2 7 0 2147483647
6 3 0 2147483647
3 7 0 2147483647
6 4 0 2147483647
4 7 0 2147483647
6 5 0 2147483647
5 7 0 2147483647
5 1 1 2147483647
3 4 1 2147483647样例输出
2数据范围与提示
1≤n≤50003,1≤m≤125003 1 \leq n \leq 50003 , 1\leq m \leq 1250031≤n≤50003,1≤m≤125003
代码：
#include <bits/stdc++.h>
using namespace std ;
#define copy( a , x ) memcpy ( a , x , sizeof a )
typedef long long LL ;
const int MAXN = 115000 ;
const int MAXE = 1000000 ;
const int MAXQ = 1000000 ;
const int INF = 0x3f3f3f3f ;
struct Edge {
int v , n ;
LL c ;
Edge ( int var = 0 , LL cap = 0 , int next = 0 ) :
v ( var ) , c ( cap ) , n ( next ) {}
} ;
struct netWork {
Edge edge[MAXE] ;
int adj[MAXN] , cntE ;
int cur[MAXN] , d[MAXN] , num[MAXN] , pre[MAXN] ;
bool vis[MAXN] ;
int Q[MAXQ] , head , tail ;
int s , t , nv ;
LL flow ;
void init () {
cntE = 0 ;
memset(adj,-1,sizeof(adj));
}
void addedge ( int u , int v , LL c , LL rc = 0 ) {
edge[cntE] = Edge ( v , c , adj[u] ) ;
adj[u] = cntE ++ ;
edge[cntE] = Edge ( u , rc , adj[v] ) ;
adj[v] = cntE ++ ;
}
void rev_Bfs () {
memset(vis,0,sizeof(vis));
memset(num,0,sizeof(num));
d[t] = 0 ;
vis[t] = 1 ;
head = tail = 0 ;
Q[tail ++] = t ;
num[0] = 1 ;
while ( head != tail ) {
int u = Q[head ++] ;
for ( int i = adj[u] ; ~i ; i = edge[i].n ) {
int v = edge[i].v ;
if ( vis[v] )
continue ;
vis[v] = 1 ;
d[v] = d[u] + 1 ;
++ num[d[v]] ;
Q[tail ++] = v ;
}
}
}
LL ISAP () {
copy ( cur , adj ) ;
rev_Bfs () ;
flow = 0 ;
int i , u = pre[s] = s ;
while ( d[s] < nv ) {
if ( u == t ) {
LL f = INF ;
int pos ;
for ( i = s ; i != t ; i = edge[cur[i]].v )
if ( f > edge[cur[i]].c )
f = edge[cur[i]].c , pos = i ;
for ( i = s ; i != t ; i = edge[cur[i]].v )
edge[cur[i]].c -= f , edge[cur[i] ^ 1].c += f ;
u = pos ;
flow += f ;
}
for ( i = cur[u] ; ~i ; i = edge[i].n )
if ( edge[i].c && d[u] == d[edge[i].v] + 1 )
break ;
if ( ~i ) {
cur[u] = i ;
pre[edge[i].v] = u ;
u = edge[i].v ;
}
else {
if ( 0 == ( -- num[d[u]] ) )
break ;
int mmin = nv ;
for ( i = adj[u] ; ~i ; i = edge[i].n )
if ( edge[i].c && mmin > d[edge[i].v] )
cur[u] = i , mmin = d[edge[i].v] ;
d[u] = mmin + 1 ;
++ num[d[u]] ;
u = pre[u] ;
}
}
return flow ;
}
} ;
int read () {
char c = ' ' ;
int x = 0 ;
while ( c < '0' || c > '9' )
c = getchar () ;
while ( c >= '0' && c <= '9' ) {
x = x * 10 + c - '0' ;
c = getchar () ;
}
return x ;
}
netWork net ;
int pp;
int n,m,k;
LL to[MAXN];
int ss,tt;
void work () {
net.init () ;
memset(to,0,sizeof(to));
net.s = n+1, net.t = net.s+1, net.nv = net.t + 1 ;
int u,v;
int L,R;
for(int i=1;i<=m;i++)
{
//u=read();v=read();L=read();R=read();
scanf("%d%d%d%d",&u,&v,&L,&R);
net.addedge(u,v,R-L);
to[u]-=L;
to[v]+=L;
}
LL sum=0;
for(int i=1;i<=n;i++)
{
if(to[i]>0)
{
net.addedge(net.s,i,to[i]);
sum+=to[i];
}
else
{
net.addedge(i,net.t,-to[i]);
}
}
LL flow =net.ISAP();
net.addedge(tt,ss,INF);
flow += net.ISAP();
if(flow==sum)
{
printf ("%lld\n",net.edge[net.cntE-1].c);
return;
}
puts("please go home to sleep");
}
int main()
{
//n=read();m=read();ss=read();tt=read();
scanf("%d%d%d%d",&n,&m,&ss,&tt);
work();
return 0;
}