2D Plane 2N Points-ATcoder092

Time limit : 2sec / Memory limit : 256MB

Score : 400 points

Problem Statement

On a two-dimensional plane, there are N red points and N blue points. The coordinates of the i-th red point are (ai,bi), and the coordinates of the i-th blue point are(ci,di).

A red point and a blue point can form a friendly pair when, the x-coordinate of the red point is smaller than that of the blue point, and the y-coordinate of the red point is also smaller than that of the blue point.

At most how many friendly pairs can you form? Note that a point cannot belong to multiple pairs.

Constraints

• All input values are integers.
• 1≤N≤100
• 0≤ai,bi,ci,di<2N
• a1,a2,…,aN,c1,c2,…,cN are all different.
• b1,b2,…,bN,d1,d2,…,dN are all different.

  #include<algorithm>
  #include<cstdio>
  #include<iostream>
  #include<vector>
  #include<cstring>
  using namespace std;
  int cnt[10008];
  int main()
  {
      int n;
      while(scanf("%d",&n)!=EOF)
      {
          vector<pair<pair<int,int>,int> > a;
          int x,y;
          for(int i=0; i<n; i++)
          {
              cin >> x>> y;
              a.push_back(make_pair(make_pair(x,y),0));
          }
          for(int i=0; i<n; i++)
          {
              cin >> x>> y;
             a.push_back(make_pair(make_pair(x,y),1));
          }
          sort(a.begin(),a.end());
          int ans=0;
          memset(cnt,0,sizeof(cnt));
          for(int i=0;i<a.size();i++){
              if(a[i].second==0)
              {
                  cnt[a[i].first.second]++;
              }
              else{
                  for(int j=a[i].first.second-1;j>=0;j--){
                      if(cnt[j]>0){
                          cnt[j]--;
                          ans++;
                          break;
                      }
                  }
              }
          }
          cout<<ans<<endl;
      }
  }