P3467(矩形覆盖问题)

#include <bits/stdc++.h>
using namespace std;
int n,a[250009],b[250009];
int q[250009],p[250009];
map<int,int>m;
int ans;
int main()
{
    cin>>n;
    int ans=0;
    for(int i=1;i<=n;i++)
        cin>>a[i]>>b[i];
    int tail=0,head=1;
    for(int i=1;i<=n;i++)
    {
        while(tail>=head&&q[tail]>=b[i])
        {
            if(q[tail]==b[i])    ans++;
            tail--;
        }
        q[++tail]=b[i],p[tail]=i;
    }
    cout<<n-ans;
}