hdu 3549 Flow Problem（最大流模板题）

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=3549

2
3 2
1 2 1
2 3 1
3 3
1 2 1
2 3 1
1 3 1

Case 1: 1
Case 2: 2

代码例如以下：

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
const int MAXN = 32;//点数的最大值
const int MAXM = 1017;//边数的最大值
const int INF = 0x3f3f3f3f;
struct Edge
{
	int to, cap, flow;
	int next;
}edge[MAXM];//注意是MAXM
int tol;
int head[MAXN];
int dep[MAXN],pre[MAXN],cur[MAXN];
int gap[MAXN];//gap[x]=y :说明残留网络中dep[i]==x的个数为y
void init()
{
	tol = 0;
	memset(head,-1,sizeof (head));
}
//加边，单向图三个參数。双向图四个參数
void addedge (int u,int v,int w,int rw=0)
{
	edge[tol].to = v;edge[tol].cap = w;
	edge[tol].next = head[u];
	edge[tol].flow = 0;
	head[u] = tol++;
	edge[tol].to = u;edge[tol].cap = rw;
	edge[tol]. next = head[v];
	edge[tol].flow = 0;head[v]=tol++;
}
//输入參数：起点、终点、点的总数
//点的编号没有影响，仅仅要输入点的总数
int sap(int start,int end, int N)
{
	memset(gap,0,sizeof(gap));
	memset(dep,0,sizeof(dep));
	memcpy(cur,head,sizeof(head));
	int u = start;
	pre[u] = -1;
	gap[0] = N;
	int ans = 0;
	int i;
	while(dep[start] < N)
	{
		if(u == end)
		{
			int Min = INF;
			for( i = pre[u];i != -1; i = pre[edge[i^1]. to])
			{
				if(Min > edge[i].cap - edge[i]. flow)
					Min = edge[i].cap - edge[i].flow;
			}
			for( i = pre[u];i != -1; i = pre[edge[i^1]. to])
			{
				edge[i].flow += Min;
				edge[i^1].flow -= Min;
			}
			u = start;
			ans += Min;
			continue;
		}
		bool flag =  false;
		int v;
		for( i = cur[u]; i != -1;i = edge[i].next)
		{
			v = edge[i]. to;
			if(edge[i].cap - edge[i].flow && dep[v]+1 == dep[u])
			{
				flag =  true;
				cur[u] = pre[v] = i;
				break;
			}
		}
		if(flag)
		{
			u = v;
			continue;
		}
		int Min = N;
		for( i = head[u]; i !=  -1; i = edge[i]. next)
		{
			if(edge[i].cap - edge[i].flow && dep[edge[i].to] < Min)
			{
				Min = dep[edge[i].to];
				cur[u] = i;
			}
		}
		gap[dep[u]]--;
		if(!gap[dep[u]]) 
			return ans;
		dep[u] = Min+1;
		gap[dep[u]]++;
		if(u != start) 
			u = edge[pre[u]^1].to;
	}
	return ans;
}
int main()
{
	int n, m;
	int a, b, w;
	int c, s, t;
	int i;
	int T;
	int cas = 0;
	scanf("%d",&T);
	while(T--)
	{
		init();//初始化    
		scanf("%d%d",&n,&m);
		for(i = 1; i <= m; i++)//边数
		{
			scanf("%d%d%d",&a,&b,&w);
			addedge(a,b,w,0);
		//	addedge(b,a,w,0);
		}
		int ans = sap(1, n, n);
		printf("Case %d: %d\n",++cas,ans);
	}
	return 0;
}