SGU194 Reactor Cooling 有下界最大流

学习别人的方法。大致是：

无源汇的最大流 ： 新建源点，汇点，sum[i]为每个点进来的下界流之和减去出去的下界流之和，如果sum[i] > 0，由源点向该点建一条边，上界为sum[i]，下界为0

如果sum[i] < 0, 由该点向汇点建边，上界为-sum[i]，下界为0。

跑一遍源点到汇点的最大流，当所有源点连得边都满流的时候存在可行流，当前的流量即为最大流。

#include <cstdio>#include <ctime>#include <cstdlib>#include <cstring>#include <queue>#include <string>#include <set>#include <stack>#include <map>#include <cmath>#include <vector>#include <iostream>#include <algorithm>#include <bitset>#include <fstream>using namespace std;//LOOP#define FF(i, a, b) for(int i = (a); i < (b); ++i)#define FE(i, a, b) for(int i = (a); i <= (b); ++i)#define FED(i, b, a) for(int i = (b); i>= (a); --i)#define REP(i, N) for(int i = 0; i < (N); ++i)#define CLR(A,value) memset(A,value,sizeof(A))#define FC(it, c) for(__typeof((c).begin()) it = (c).begin(); it != (c).end(); it++)//OTHER#define SZ(V) (int)V.size()#define PB push_back#define MP make_pair#define all(x) (x).begin(),(x).end()//INPUT#define RI(n) scanf("%d", &n)#define RII(n, m) scanf("%d%d", &n, &m)#define RIII(n, m, k) scanf("%d%d%d", &n, &m, &k)#define RIV(n, m, k, p) scanf("%d%d%d%d", &n, &m, &k, &p)#define RV(n, m, k, p, q) scanf("%d%d%d%d%d", &n, &m, &k, &p, &q)#define RS(s) scanf("%s", s)//OUTPUT#define WI(n) printf("%d\n", n)#define WS(n) printf("%s\n", n)//debug//#define online_judge#ifndef online_judge#define dt(a)  << (#a) << "=" << a << " "#define debugI(a) cout dt(a) << endl#define debugII(a, b) cout dt(a) dt(b) << endl#define debugIII(a, b, c) cout dt(a) dt(b) dt(c) << endl#define debugIV(a, b, c, d) cout dt(a) dt(b) dt(c) dt(d) << endl#define debugV(a, b, c, d, e) cout dt(a) dt(b) dt(c) dt(d) dt(e) << endl#else#define debugI(v)#define debugII(a, b)#define debugIII(a, b, c)#define debugIV(a, b, c, d)#endif#define sqr(x) (x) * (x)typedef long long LL;typedef unsigned long long ULL;typedef vector <int> VI;const double eps = 1e-9;const int MOD = 1000000007;const double PI = acos(-1.0);const int INF = 0x3f3f3f3f;const int maxn = 100010;struct Edge{    int from, to, cap, flow, lcap;};int n, m, s, t;vector<Edge> edges;VI G[maxn];bool vis[maxn];int d[maxn], cur[maxn];void init(){    REP(i, n + 1)   G[i].clear();    edges.clear();}void addEdge(int from, int to, int cap, int lcap){    edges.PB((Edge){from, to, cap, 0, lcap});    edges.PB((Edge){to, from, 0, 0, -lcap});    m = edges.size();    G[from].PB(m - 2);    G[to].PB(m - 1);}bool bfs(){    CLR(vis, 0);    queue<int> Q;    Q.push(s);    d[s] = 0, vis[s] = 1;    while (!Q.empty())    {        int u = Q.front(); Q.pop();        REP(i, G[u].size())        {            Edge& e = edges[G[u][i]];            if (!vis[e.to] && e.cap > e.flow)            {                vis[e.to] = 1;                d[e.to] = d[u] + 1;                Q.push(e.to);            }        }    }    return vis[t];}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;}int maxflow(int ss, int tt){    s = ss, t = tt;    int flow = 0;    while (bfs())    {        CLR(cur, 0);        flow += dfs(s, INF);    }    return flow;}int sum[maxn];int main(){    //freopen("0.txt", "r", stdin);    int nodenum, edgenum;    int u, v, l, c;    int se, te;    while (~RII(nodenum, edgenum))    {        CLR(sum, 0);        n = nodenum + 2;        init();        REP(i, edgenum)        {            RIV(u, v, l, c);            addEdge(u, v, c - l, l);            sum[u] -= l;            sum[v] += l;        }        se = edges.size(), te = se;        FE(i, 1, nodenum)            if (sum[i] > 0)                addEdge(0, i, sum[i], 0), te = edges.size();        FE(i, 1, nodenum)            if (sum[i] < 0)                addEdge(i, nodenum + 1, -sum[i], 0);        int maxf = maxflow(0, nodenum + 1);//        debugI(maxf);//        debugII(se, te);        bool f = 0;        for (int i = se; i < te; i += 2)            if (edges[i].flow < edges[i].cap)            {                f = 1;                break;            }        if (f)            puts("NO");        else        {            puts("YES");//            REP(i, edges.size())            for (int i = 0; i < se; i += 2)                printf("%d\n", edges[i].flow + edges[i].lcap);        }    }    return 0;}