AtCoder Beginner Contest 091 C - 2D Plane 2N Points

C - 2D Plane 2N Points

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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≤a i , b i , c i , d i<2 N
• a1,a2,…,aN,c1,c2,…,cN are all different.
• b1,b2,…,bN,d1,d2,…,dN are all different.

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Input

Input is given from Standard Input in the following format:

N
a1 b1
a2 b2
:
aN bN
c1 d1
c2 d2
:
cN dN

Output

Print the maximum number of friendly pairs.

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Sample Input 1

Copy

3
2 0
3 1
1 3
4 2
0 4
5 5

Sample Output 1

Copy

2

For example, you can pair (2,0) and (4,2), then (3,1) and (5,5).

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Sample Input 2

Copy

3
0 0
1 1
5 2
2 3
3 4
4 5

Sample Output 2

Copy

2

For example, you can pair (0,0) and (2,3), then (1,1) and (3,4).

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Sample Input 3

Copy

2
2 2
3 3
0 0
1 1

Sample Output 3

Copy

0

It is possible that no pair can be formed.

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Sample Input 4

Copy

5
0 0
7 3
2 2
4 8
1 6
8 5
6 9
5 4
9 1
3 7

Sample Output 4

Copy

5

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Sample Input 5

Copy

5
0 0
1 1
5 5
6 6
7 7
2 2
3 3
4 4
8 8
9 9

Sample Output 5

Copy

4

这题说实在我也不太明白，后来把两组分别以x，y做升序和降序居然ac了，不可思议，后来学弟和我说这其实是利用了找两个点最接近的原理，玄学+谜