HDU3157 Crazy Circuits & BZOJ 2502 清理雪道（有下界最小流）

BZOJ上已經沒有這道題了，uva1440和這道題類似，但要輸出答案

方法:

1.新建源匯SS,TT,按有上下界的方法建圖.

2.做一次SS->TT的最大流.

3.原圖中的匯點T向原圖中的源點S連一條inf的邊.

4.再做一次SS>TT的最大流就是答案.

#include <bits/stdc++.h>
using namespace std;
const int MAXN = 100005;
const int MAXM = 110005;
const int INF = 0x3f3f3f3f;
struct Edge1
{
	int from,to,cap,flow;
};
struct Dinic
{
	int n,m,s,t;
	vector<Edge1> edges;
	vector<int> G[MAXN];
	bool vis[MAXN];
	int d[MAXN];
	int cur[MAXN];
	void init(int n)
	{
		this -> n = n;
		for(int i = 0; i <= n + 1; i++){
			G[i].clear();
		}
		edges.clear();
	}
	void AddEdge(int from,int to,int cap)
	{
		edges.push_back((Edge1){from,to,cap,0});
		edges.push_back((Edge1){to,from,0,0});
		m = edges.size();
		G[from].push_back(m - 2);
		G[to].push_back(m - 1);
	}
	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++) {
				Edge1& 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];
	}
	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++) {
			Edge1& 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 s,int t) {
		this -> s = s,this -> t = t;
		int flow = 0;
		while(BFS()) {
			memset(cur,0,sizeof(cur));
			flow += DFS(s,INF);
		}
		return flow;
	}
}din;
int n,num,temp,S,T,SS,TT,ans;
int in[MAXN],out[MAXN];
int main(void)
{
    while(scanf("%d",&n) != EOF) {
        memset(in,0,sizeof(in));
        memset(out,0,sizeof(out));
        S = 0,T = n + 1;
        SS = n + 2,TT = n + 3;
        din.init(n + 4);
        for(int i = 1; i <= n; i++) {
            scanf("%d",&num);
            for(int j = 1; j <= num; j++) {
                scanf("%d",&temp);
                din.AddEdge(i,temp,INF);
                out[i]++;
                in[temp]++;
            }
        }
        for(int i = 1; i <= n; i++) {
            din.AddEdge(S,i,INF);
            din.AddEdge(i,T,INF);
        }
        for(int i = 1; i <= n; i++) {
            din.AddEdge(SS,i,in[i]);
            din.AddEdge(i,TT,out[i]);
        }
        ans = din.Maxflow(SS,TT);
        din.AddEdge(T,S,INF);
        ans = din.Maxflow(SS,TT);
        printf("%d\n",ans);
    }
    return 0;
}
/*
8
1 3
1 7
2 4 5
1 8
1 8
0
2 6 5
0
*/

HDU 3157 ：http://acm.hdu.edu.cn/showproblem.php?pid=3157

#include <bits/stdc++.h>
using namespace std;
const int MAXN = 1000;
const int MAXM = 2005;
const int INF = 0x3f3f3f3f;
struct Edge1
{
	int from,to,cap,flow;
};
struct Dinic
{
	int n,m,s,t;
	vector<Edge1> edges;
	vector<int> G[MAXN];
	bool vis[MAXN];
	int d[MAXN];
	int cur[MAXN];
	void init(int n)
	{
		this -> n = n;
		for(int i = 0; i <= n + 1; i++){
			G[i].clear();
		}
		edges.clear();
	}
	void AddEdge(int from,int to,int cap)
	{
		edges.push_back((Edge1){from,to,cap,0});
		edges.push_back((Edge1){to,from,0,0});
		m = edges.size();
		G[from].push_back(m - 2);
		G[to].push_back(m - 1);
	}
	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++) {
				Edge1& 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];
	}
	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++) {
			Edge1& 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 s,int t) {
		this -> s = s,this -> t = t;
		int flow = 0;
		while(BFS()) {
			memset(cur,0,sizeof(cur));
			flow += DFS(s,INF);
		}
		return flow;
	}
}din;
int n,m,S,T,SS,TT,w,u,v,len,ans;
int in[MAXN],out[MAXN];
char s1[20],s2[20];
bool check()
{
    for(int i = 0; i < din.edges.size(); i++) {
        Edge1 e = din.edges[i];
        if((e.from == SS || e.to == TT) && e.cap != e.flow) return false;
    }
    return true;
}
int main(void)
{
    while(scanf("%d %d",&n,&m) != EOF && (n + m)) {
        memset(in,0,sizeof(in));
        memset(out,0,sizeof(out));
        S = 0,T = n + 1;
        SS = n + 2,TT = n + 3;
        din.init(n + 4);
        for(int i = 1; i <= m; i++) {
            scanf("%s %s %d",s1,s2,&w);
            if(s1[0] == '+') u = S;
            else {
                u = 0;
                len = strlen(s1);
                for(int j = 0; j < len; j++) {
                    u = u * 10 + s1[j] - '0';
                }
            }
            if(s2[0] == '-') v = T;
            else {
                v = 0;
                int len = strlen(s2);
                for(int j = 0; j < len; j++) {
                    v = v * 10 + s2[j] - '0';
                }
            }
            in[v] += w;
            out[u] += w;
            din.AddEdge(u,v,INF);
            //printf("%d %d %d----\n",u,v,w);
        }
        for(int i = 0; i <= n + 1; i++) {
            din.AddEdge(SS,i,in[i]);
            din.AddEdge(i,TT,out[i]);
        }
        din.Maxflow(SS,TT);
        din.AddEdge(T,S,INF);
        ans = din.Maxflow(SS,TT);
        if(check()) printf("%d\n",ans);
        else printf("impossible\n");
    }
    return 0;
}
/*
8
1 3
1 7
2 4 5
1 8
1 8
0
2 6 5
0
*/