loj #117. 有源汇有上下界最小流

题目链接

有源汇有上下界最小流，->上下界网络流

注意细节，边数组也要算上后加到SS，TT边。

 #include<cstdio>
 #include<algorithm>
 #include<cmath>
 #include<cstring>
 #include<iostream>

 using namespace std;

 const int N = ;
 const int INF = 1e9;

 struct Edge{
     int to,nxt,c;
 }e[];
 int head[N],dis[N],cur[N],M[N];
 int q[],L,R;
 int tot = ,n,m,S,T,Sum;

 inline char nc() {
     static char buf[],*p1 = buf,*p2 = buf;
     return p1==p2&&(p2=(p1=buf)+fread(buf,,,stdin),p1==p2)?EOF:*p1++;
 }
 inline int read() {
     int x = ,f = ;char ch = nc();
     for (; ch<''||ch>'';ch=nc()) if(ch=='-') f=-;
     for (; ch>=''&&ch<=''; ch=nc()) x=x*+ch-'';
     return x * f;
 }
 void add_edge(int u,int v,int c) {
     e[++tot].to = v,e[tot].c = c,e[tot].nxt = head[u],head[u] = tot;
 }
 bool bfs() {
     for (int i=; i<=n+; ++i)
         cur[i] = head[i],dis[i] = -;
     L = ,R = ;
     q[++R] = S;
     dis[S] = ;
     while (L <= R) {
         int u = q[L++];
         for (int i=head[u]; i; i=e[i].nxt) {
             int v = e[i].to;
             if (dis[v] == - && e[i].c > ) {
                 dis[v] = dis[u] + ;
                 q[++R] = v;
                 if (v == T) return true;
             }
         }
     }
     return false;
 }
 int dfs(int u,int flow) {
     if (u == T) return flow;
     int used = ;
     for (int &i=cur[u]; i; i=e[i].nxt) {
         int v = e[i].to;
         if (dis[v] == dis[u] +  && e[i].c > ) {
             int tmp = dfs(v,min(e[i].c,flow-used));
             if (tmp > ) {
                 e[i].c -= tmp;e[i^].c += tmp;
                 used += tmp;
                 if (used == flow) break;
             }
         }
     }
     if (used != flow) dis[u] = -;
     return used;
 }
 int dinic(int s,int t) {
     S = s,T = t;
     int ans = ;
     while (bfs()) ans += dfs(S,INF);
     return ans;
 }
 int main () {
     n = read(),m = read();
     int s = read(),t = read();
     int ss = n + ,tt = n + ;
     for (int i=; i<=m; ++i) {
         int u = read(),v = read(),b = read(),c = read();
         add_edge(u,v,c-b);
         add_edge(v,u,);
         M[u] -= b;M[v] += b;
     }
     for (int i=; i<=n; ++i) {
         if (M[i] > ) add_edge(ss,i,M[i]),add_edge(i,ss,),Sum += M[i];
         if (M[i] < ) add_edge(i,tt,-M[i]),add_edge(tt,i,);
     }
     add_edge(t,s,INF); //-
     add_edge(s,t,);
     if (dinic(ss,tt) != Sum) {
         printf("please go home to sleep");
         return ;
     }
     int ans = e[tot].c;
     e[tot].c = ;e[tot ^ ].c = ;
     ans -= dinic(t,s);
     printf("%d",ans);
     return ;
 }