萌新刚学单调队列求助

#include<bits/stdc++.h>
using namespace std;
int n,d,maxx,ans=-1,h[1000010];
int head=1,tail,q[1000010][2];
int maxi[1000010],mini[1000010];
struct point
{
	int x,y;
}a[100010];
bool check(int w)
{
	head=1,tail=0;
	memset(q,0,sizeof(q));
	for(int i=1;i<=maxx;i++)
	{
		while(head<=tail&&q[tail][0]<=h[i])tail--;
		q[++tail][0]=h[i];q[tail][1]=i;
		while(head<=tail&&q[tail][1]-q[head][1]>w)head++;
		maxi[i]=q[head][0];
	}
	head=1,tail=0;
	memset(q,0,sizeof(q));
	for(int i=1;i<=maxx;i++)
	{
		while(head<=tail&&q[tail][0]>=h[i])tail--;
		while(head<=tail&&q[tail][1]-q[head][1]>w)head++;
		if(!h[i])continue;
		q[++tail][0]=h[i];q[tail][1]=i;
		mini[i]=q[head][0];
	}
	for(int i=1;i<=maxx;i++)
		if(maxi[i]-mini[i]>=d&&mini[i])return 1;
	return 0;
}
int main()
{
	scanf("%d%d",&n,&d);
	for(int i=1;i<=n;i++)scanf("%d%d",&a[i].x,&a[i].y);
	for(int i=1;i<=n;i++)h[a[i].x]=a[i].y,maxx=max(maxx,a[i].x);
	int l=0,r=1e6,mid;
	while(l<=r)
	{
		mid=(l+r)>>1;
		if(check(mid))r=mid-1,ans=mid;
		else l=mid+1;
	}
	printf("%d",ans);
	return 0;
}