HDU 4268 multiset

http://acm.hust.edu.cn/vjudge/contest/123100#problem/B

#include <iostream>
#include <string>
#include <cstring>
#include <cstdlib>
#include <cstdio>
#include <cmath>
#include <algorithm>
#include <stack>
#include <queue>
#include <cctype>
#include <vector>
#include <iterator>
#include <set>
#include <map>
#include <sstream>
using namespace std;

#define mem(a,b) memset(a,b,sizeof(a))
#define pf printf
#define sf scanf
#define spf sprintf
#define pb push_back
#define debug printf("!
")
#define MAXN 100000 + 10
#define MAX(a,b) a>b?a:b
#define blank pf("
")
#define LL long long
#define ALL(x) x.begin(),x.end()
#define INS(x) inserter(x,x.begin())
#define pqueue priority_queue
#define INF 0x3f3f3f3f

int n,m;

struct node
{
    int h,w;
}a[200005],b[200005];

bool cmp(node x,node y)
{
    return x.h < y.h;
}

multiset<int> mt;
multiset<int>::iterator it;

int main()
{
    int i,j;
    int t;
    sf("%d",&t);
    while(t--)
    {
        sf("%d",&n);
        for(i=1;i<=n;i++)
        {
            sf("%d%d",&a[i].h,&a[i].w);
        }
        for(i=1;i<=n;i++)
        {
            sf("%d%d",&b[i].h,&b[i].w);
        }
        sort(a+1,a+n+1,cmp);
        sort(b+1,b+n+1,cmp);

        mt.clear();

        int cnt=0;
        for(i=1,j=1;i<=n;i++)
        {
            while(j<=n && a[i].h>=b[j].h)
            {
                mt.insert(b[j].w);
                j++;
            }
            if(mt.empty()) continue;
            it = mt.upper_bound(a[i].w);
            if(it!=mt.begin()) it--;
            if((*it) <= a[i].w)
            {
                cnt++;
                mt.erase(it);
            }
        }
        pf("%d
",cnt);

    }
    return 0;
}