zoukankan      html  css  js  c++  java
  • [Usaco2005 Nov]Asteroids

    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.
    矩阵上有一些小行星,占据了一些格子,我们每次操作可以清理一列中的所有小行星,也可以清理一行中的所有小行星,问最少进行多少次操作可以清理掉所有的小行星。

    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 4
    1 1
    1 3
    2 2
    3 2

    INPUT DETAILS:
    The following diagram represents the data, where "X" is an
    asteroid and "." is empty space:
    X.X
    .X.
    .X.

    Sample Output
    2

    OUTPUT DETAILS:
    Bessie may fire across row 1 to destroy the asteroids at (1,1) and
    (1,3), and then she may fire down column 2 to destroy the asteroids
    at (2,2) and (3,2).


    二分图匹配,对于每个点,它若被行清理过,就不必再次被列清理,反之亦然,然后就是最大匹配

    /*program from Wolfycz*/
    #include<cmath>
    #include<cstdio>
    #include<cstring>
    #include<iostream>
    #include<algorithm>
    #define inf 0x7f7f7f7f
    using namespace std;
    typedef long long ll;
    typedef unsigned int ui;
    typedef unsigned long long ull;
    inline int read(){
    	int x=0,f=1;char ch=getchar();
    	for (;ch<'0'||ch>'9';ch=getchar())	if (ch=='-')    f=-1;
    	for (;ch>='0'&&ch<='9';ch=getchar())	x=(x<<1)+(x<<3)+ch-'0';
    	return x*f;
    }
    inline void print(int x){
    	if (x>=10)     print(x/10);
    	putchar(x%10+'0');
    }
    const int N=5e2;
    int path[N+10],pre[N*N+10],now[N+10],child[N*N+10];
    int tot,n,m;
    bool use[N+10];
    void join(int x,int y){pre[++tot]=now[x],now[x]=tot,child[tot]=y;}
    bool check(int x){
        for (int p=now[x],son=child[p];p;p=pre[p],son=child[p]){
            if (use[son])   continue;
            use[son]=1;
            if (path[son]<0||check(path[son])){path[son]=x;return 1;}
        }
        return 0;
    }
    void work(){
        memset(path,-1,sizeof(path));
        int res=0;
        for (int i=1;i<=n;i++){
            memset(use,0,sizeof(use));
            if (check(i))   res++;
        }
        printf("%d
    ",res);
    }
    int main(){
        n=read(),m=read();
        for (int i=1;i<=m;i++){
            int x=read(),y=read();
            join(x,y);
        }
        work();
        return 0;
    }
    
  • 相关阅读:
    掌游 新项目:我采用NH连接MySql所遇到的问题
    运行时动态将字符串编译为C#可执行代码
    数据库连接字符串用IP死活连不上,只能用计算机名连,ADO或ORM错误提示为表“对象”无效
    File.Copy是Copy完再执行下一句的,自己验证过了。
    window.external.XXX 判断是否有这个方法
    java构建工具——ant使用
    大数据学习之路(1)Hadoop生态体系结构
    Java经典代码片段——使用NIO进行快速的文件拷贝
    Java代码片段——向文件末尾添加内容
    JAVA几种常见的编码格式(转)
  • 原文地址:https://www.cnblogs.com/Wolfycz/p/8422067.html
Copyright © 2011-2022 走看看