Poj 3041 asteroids (binary matching template)

Question link: http://poj.org/problem? Id = 3041

Description

Bessie wants to navigate her spaceship through a dangerous asteroid field in the shape of an n x n grid (1 <= n <= 500 ). the grid contains k asteroids (1 <= k <= 10,000), which are conveniently located at the lattice points of the grid.

Fortunately, Bessie has a powerful weapon that can vaporize all the asteroids in any given row or column of the grid with a single shot. this weapon is quite expensive, so she wishes to use it sparingly. given the location of all the asteroids in the field, find the minimum number of shots Bessie needs to fire to eliminate all of the asteroids.

Input

* Line 1: two integers N and K, separated by a single space.
* Lines 2 .. k + 1: Each line contains two space-separated integers R and C (1 <= r, C <= N) denoting the row and column coordinates of an asteroid, respectively.

Output

* Line 1: The integer representing the minimum number of times Bessie must shoot.

Sample Input

3 41 11 32 23 2

Sample output

2

Hint

Input details:
The following dimo-represents the data, where "X" is an asteroid and "." Is empty space:
X. x
. X.
. X. 

Output details:
Bessie may fire your SS Row 1 to destroy the asteroids at () and (), and then she may fire down column 2 to destroy the asteroids at () and ).

Source

Usaco 2005 November gold

Question:

A matrix of N * n, which contains M minor planets. Each weapon can eliminate one or more minor series.
Q: Is there a minimum number of weapons used to destroy all planets?

The Code is as follows:

# Include <cstdio> # include <cstring> # include <algorithm> # include <iostream> using namespace STD; # define maxn 517int N; int G [maxn] [maxn], linker [maxn]; bool used [maxn]; int DFS (int l) // find the augmented path {int R; For (r = 1; r <= N; r ++) // The vertex number starts from 0. To start from 1, modify {If (G [l] [r]! = 0 &&! Used [R]) {// find the augmented path, reverse used [R] = true; If (linker [R] =-1 | DFS (linker [R]) {linker [R] = L; return 1 ;}} return 0; // do not forget this, often forget this sentence} int Hungary () {int res = 0; int L; memset (linker,-1, sizeof (linker); For (L = 1; L <= N; l ++) {memset (used, 0, sizeof (used); If (DFS (l )! = 0) RES ++;} return res;} int main () {int K, res, L, R; while (~ Scanf ("% d", & N, & K) {memset (G, 0, sizeof (g); For (INT I = 1; I <= K; I ++) {scanf ("% d", & L, & R); G [l] [r] = 1 ;} res = Hungary (); printf ("% d \ n", Res);} return 0 ;}

Poj 3041 asteroids (binary matching template)