网络流

Posted 2020-11-09 DukeLv

#include<iostream>
#include<cstdio>
#include<queue>
#include<cstring>
using namespace std;
struct node
{
	int x,y,c,next,other;
};
node a[2110000];
int len = 0,last[5000],st,ed;
int list[5000]; 
queue <int> qu;
void add(int x,int y,int w)
{
	int k1,k2;
	a[++len].next = last[x];
	k1 = len;
	a[len].x = x;
	a[len].y = y;
	a[len].c = w;
	last[x] = len;
	a[++len].next = last[y];
	k2 = len;
	a[len].x = y;
	a[len].y = x;
	a[len].c = 0;
	last[y] = len;
	a[k1].other = k2;
	a[k2].other = k1;
}
int h[5000];
bool bfs()
{
	memset(h,0,sizeof(h));
	h[st] = 1;
	int head,tail;
	list[1] = st;
	head = 1;
	tail = 2;
	while(head != tail)
	{
		int x = list[head];
//		cout<<x<<endl;
		for(int k = last[x];k;k = a[k].next)
		{
			int y = a[k].y;
//			cout<<k<<" "<<a[k].c<<" "<<y<<endl;
			if(a[k].c > 0 && h[y] == 0)
			{
				h[y] = h[x] + 1;
				list[tail++] = y;
//				cout<<y<<endl;
			}
		}
		head++;
	}
	/*for(int i = 1;i <= ed;i++)
	cout<<h[i]<<" ";
	cout<<endl;
	for(int i = 1;i <= len;i++)
	cout<<a[i].c<<" "; 
	cout<<endl;*/
	if(h[ed] > 0)
	return true;
	else
	return false;
}
int mymin(int x,int y){return x < y ? x : y;}
int find(int x,int f)
{
	if(x == ed)
	return f;
	int s = 0,t;
	for(int k = last[x];k;k = a[k].next)
	{
		int y = a[k].y;
		if(s < f && h[y] == (h[x] + 1) && a[k].c > 0)
		{
//			cout<<a[k].c<<" "<<f - s<<endl;
			t = find(y,mymin(a[k].c,f - s));
			s += t;
//			cout<<t<<endl;
			a[k].c -= t;
			a[a[k].other].c += t;
//			cout<<k<<"_"<<a[k].c<<" "<<a[k].other<<"_"<<a[a[k].other].c<<endl;
		}
	}
	if(s == 0)
	h[x] = 0;
	return s;
}
int main()
{
	int n,m;
	cin>>m>>n;
	st = 1;
	ed = n;
	len = 0;
	memset(last,0,sizeof(last)); 
	for(int i = 1;i <= m;i++)
	{
		int x,y,z;
		cin>>x>>y>>z;
		add(x,y,z);
	}
//	cout<<endl;
	int s = 0,t;int l = 0;
	while(bfs() == true)
	{
		s += find(st,99999999);
		if(l > 10)
		break;
		l++;
	}
	cout<<s;
	return 0;
}
/*
4 4
1 2 10
2 4 5
2 3 20
3 4 10
*/