SGU 194 Reactor Cooling

#include<cstdio>
#include<cstring>
#include<string>
#include<cmath>
#include<vector>
#include<queue>
#include<algorithm>
using namespace std;


const int maxn=1000+10;
const int INF=0x7FFFFFFF;

struct Edge
{
    int from,to,cap,flow,up,low;
};
vector<Edge>edges;
vector<int>G[maxn];
bool vis[maxn];
int d[maxn];
int cur[maxn];
int Out[maxn],In[maxn];
int s,t;

//求出层次网络
bool BFS()
{
    memset(vis,0,sizeof(vis));
    queue<int>Q;
    Q.push(s);
    d[s]=0;
    vis[s]=1;
    while(!Q.empty())
    {
        int x=Q.front();
        Q.pop();
        for(int i=0; i<G[x].size(); i++)
        {
            Edge& e=edges[G[x][i]];
            if(!vis[e.to]&&e.cap>e.flow)
            {
                vis[e.to]=1;
                d[e.to]=d[x]+1;
                Q.push(e.to);
            }
        }
    }
    return vis[t];
}


//加边
void AddEdge(int from,int to,int low,int up)
{
    int m;
    Edge r;
    r.from=from;
    r.to=to;
    r.cap=up-low;
    r.flow=0;
    r.low=low;
    r.up=up;
    edges.push_back(r);
    Edge d;
    d.from=to;
    d.to=from;
    d.cap=0;
    d.flow=0;
    //r.low=low;r.up=up;
    edges.push_back(d);
    m=edges.size();
    G[from].push_back(m-2);
    G[to].push_back(m-1);
}

//每个阶段来一次DFS增广
int DFS(int x,int a)
{
    if(x==t||a==0) return a;
    int flow=0,f;
    for(int i=cur[x]; i<G[x].size(); i++)
    {
        Edge& e=edges[G[x][i]];
        if(d[x]+1==d[e.to]&&(f=DFS(e.to,min(a,e.cap-e.flow)))>0)
        {
            e.flow+=f;
            edges[G[x][i]^1].flow-=f;
            flow+=f;
            a-=f;
            if(a==0) break;
        }
    }
    return flow;
}

//多个阶段，多次建立层次网络。
int Maxflow(int ss,int tt)
{
    int flow=0;
    while(BFS())
    {
        memset(cur,0,sizeof(cur));
        flow+=DFS(ss,INF);
    }
    return flow;
}


int main()
{
    int N,M,i,j;
    while(~scanf("%d%d",&N,&M))
    {

        edges.clear();
        for(int i=0; i<maxn; i++) G[i].clear();
        memset(In,0,sizeof(In));
        memset(Out,0,sizeof(Out));
        s=0;
        t=N+1;

        for(i=1; i<=M; i++)
        {
            int u,v,low,up;
            scanf("%d%d%d%d",&u,&v,&low,&up);
            AddEdge(u,v,low,up);
            In[v]=In[v]+low;
            Out[u]=Out[u]+low;
        }

        for(i=1; i<=N; i++)
        {
            AddEdge(i,t,0,Out[i]);
            AddEdge(s,i,0,In[i]);
        }

        Maxflow(s,t);

        int flag=1;
        for(i=0; i<edges.size(); i++)
            if(edges[i].from==s)
                if(edges[i].flow<edges[i].cap)
                {
                    flag=0;
                    break;
                }
        if(!flag) printf("NO\n");
        else
        {
            printf("YES\n");
            for(i=0; i<2*M; i++)
                if(i%2==0)
                    printf("%d\n",edges[i].flow+edges[i].low);
        }
    }
    return 0;
}