Language: C++

#include <cstdio>
#include <cstring>
#include <algorithm>

using namespace std;

const int inf=10000000;

int edge[2000000],next[2000000],flow[2000000],first[1000000];
int g[1000000],h[1000000];
int i,m,n,s,x,y,head,tail,sum_edge;

inline void addedge(int x,int y,int f)
{
	sum_edge++,edge[sum_edge]=y,next[sum_edge]=first[x],flow[sum_edge]=f,first[x]=sum_edge;
	return;
}

inline int oppedge(int x)
{
	return ((x-1)^1)+1;
}

inline void buildgraph()
{
	scanf("%d%d",&n,&m);
	for (i=1;i<=m;i++)
	{
		if (i<m)
			addedge(i,i+1,inf),addedge(i+1,i,0);
		if (i<m)
			addedge(m+i+1,m+i,inf),addedge(m+i,m+i+1,0);
		addedge(i,m+m+i,inf),addedge(m+m+i,i,0);
		addedge(m+i,m+m+i,inf),addedge(m+m+i,m+i,0);
		addedge(m+m+i,m+m+m+n+1,1),addedge(m+m+m+n+1,m+m+i,0);
	}
	for (i=1;i<=n;i++)
	{
		scanf("%d%d",&x,&y);
		addedge(0,m+m+m+i,1),addedge(m+m+m+i,0,0);
		if (x>0)
			addedge(m+m+m+i,m+x,inf),addedge(m+x,m+m+m+i,0);
		if (y<=m)
			addedge(m+m+m+i,y,inf),addedge(y,m+m+m+i,0);
	}
	return;
}

inline int dinic_bfs()
{
	memset(h,0,sizeof(h));
	tail=1,g[tail]=0,h[g[tail]]=1;
	for (head=1;head<=tail;head++)
		for (i=first[g[head]];i!=0;i=next[i])
			if ((flow[i]) && (! h[edge[i]]))
				tail++,g[tail]=edge[i],h[g[tail]]=h[g[head]]+1;
	return h[m+m+m+n+1];
}

inline int dinic_dfs(int now,int cap)
{
	if (now==m+m+m+n+1)
		return cap;
	int s=0,t=0;
	for (int i=first[now];i!=0;i=next[i])
		if ((flow[i]) && (h[edge[i]]==h[now]+1))
		{
			t=dinic_dfs(edge[i],min(cap,flow[i]));
			s=s+t,cap=cap-t;
			flow[i]=flow[i]-t,flow[oppedge(i)]=flow[oppedge(i)]+t;
			if (! cap)
				break;
		}
	if (! s)
		h[now]=0;
	return s;
}

inline void maxflow()
{
	while (dinic_bfs())
		s=s+dinic_dfs(0,inf);
	printf("%d",n-s);
	return;
}

int main()
{
	buildgraph();
	maxflow();
	return 0;
}

Compiler output:
a.cc: In function 'void addedge(int, int, int)':
a.cc:15:37: error: reference to 'next' is ambiguous
   15 |         sum_edge++,edge[sum_edge]=y,next[sum_edge]=first[x],flow[sum_edge]=f,first[x]=sum_edge;
      |                                     ^~~~
In file included from /usr/include/c++/14/bits/stl_algobase.h:66,
                 from /usr/include/c++/14/algorithm:60,
                 from a.cc:3:
/usr/include/c++/14/bits/stl_iterator_base_funcs.h:232:5: note: candidates are: 'template<class _InputIterator> constexpr _InputIterator std::next(_InputIterator, typename iterator_traits<_Iter>::difference_type)'
  232 |     next(_InputIterator __x, typename
      |     ^~~~
a.cc:9:19: note:                 'int next [2000000]'
    9 | int edge[2000000],next[2000000],flow[2000000],first[1000000];
      |                   ^~~~
a.cc: In function 'int dinic_bfs()':
a.cc:54:46: error: reference to 'next' is ambiguous
   54 |                 for (i=first[g[head]];i!=0;i=next[i])
      |                                              ^~~~
/usr/include/c++/14/bits/stl_iterator_base_funcs.h:232:5: note: candidates are: 'template<class _InputIterator> constexpr _InputIterator std::next(_InputIterator, typename iterator_traits<_Iter>::difference_type)'
  232 |     next(_InputIterator __x, typename
      |     ^~~~
a.cc:9:19: note:                 'int next [2000000]'
    9 | int edge[2000000],next[2000000],flow[2000000],first[1000000];
      |                   ^~~~
a.cc: In function 'int dinic_dfs(int, int)':
a.cc:65:38: error: reference to 'next' is ambiguous
   65 |         for (int i=first[now];i!=0;i=next[i])
      |                                      ^~~~
/usr/include/c++/14/bits/stl_iterator_base_funcs.h:232:5: note: candidates are: 'template<class _InputIterator> constexpr _InputIterator std::next(_InputIterator, typename iterator_traits<_Iter>::difference_type)'
  232 |     next(_InputIterator __x, typename
      |     ^~~~
a.cc:9:19: note:                 'int next [2000000]'
    9 | int edge[2000000],next[2000000],flow[2000000],first[1000000];
      |                   ^~~~