BZOJ1731:[USACO]Layout 排队布局(差分约束)
Description
Like everyone else, cows like to stand close to their friends when queuing for feed. FJ has N (2 <= N <= 1,000) cows numbered 1..N standing along a straight line waiting for feed. The cows are standing in the same order as they are numbered, and since they can be rather pushy, it is possible that two or more cows can line up at exactly the same location (that is, if we think of each cow as being located at some coordinate on a number line, then it is possible for two or more cows to share the same coordinate). Some cows like each other and want to be within a certain distance of each other in line. Some really dislike each other and want to be separated by at least a certain distance. A list of ML (1 <= ML <= 10,000) constraints describes which cows like each other and the maximum distance by which they may be separated; a subsequent list of MD constraints (1 <= MD <= 10,000) tells which cows dislike each other and the minimum distance by which they must be separated. Your job is to compute, if possible, the maximum possible distance between cow 1 and cow N that satisfies the distance constraints.
当排队等候喂食时,奶牛喜欢和它们的朋友站得靠近些。FJ有N(2<=N<=1000)头奶牛,编号从1到N,沿一条直线站着等候喂食。奶牛排在队伍中的顺序和它们的编号是相同的。因为奶牛相当苗条,所以可能有两头或者更多奶牛站在同一位置上。即使说,如果我们想象奶牛是站在一条数轴上的话,允许有两头或更多奶牛拥有相同的横坐标。一些奶牛相互间存有好感,它们希望两者之间的距离不超过一个给定的数L。另一方面,一些奶牛相互间非常反感,它们希望两者间的距离不小于一个给定的数D。给出ML条关于两头奶牛间有好感的描述,再给出MD条关于两头奶牛间存有反感的描述。(1<=ML,MD<=10000,1<=L,D<=1000000)你的工作是:如果不存在满足要求的方案,输出-1;如果1号奶牛和N号奶牛间的距离可以任意大,输出-2;否则,计算出在满足所有要求的情况下,1号奶牛和N号奶牛间可能的最大距离。
Input
* Line 1: Three space-separated integers: N, ML, and MD. * Lines 2..ML+1: Each line contains three space-separated positive integers: A, B, and D, with 1 <= A < B <= N. Cows A and B must be at most D (1 <= D <= 1,000,000) apart. * Lines ML+2..ML+MD+1: Each line contains three space-separated positive integers: A, B, and D, with 1 <= A < B <= N. Cows A and B must be at least D (1 <= D <= 1,000,000) apart.
Output
* Line 1: A single integer. If no line-up is possible, output -1. If cows 1 and N can be arbitrarily far apart, output -2. Otherwise output the greatest possible distance between cows 1 and N.
Sample Input
1 3 10
2 4 20
2 3 3
INPUT DETAILS:
There are 4 cows. Cows #1 and #3 must be no more than 10 units
apart, cows #2 and #4 must be no more than 20 units apart, and cows
#2 and #3 dislike each other and must be no fewer than 3 units apart.
Sample Output
四只牛分别在0,7,10,27.
Solution
Code
#include<iostream>
#include<cstring>
#include<cstdlib>
#include<cstdio>
#include<queue>
#define N (200000+100)
#define INF (2000000000)
using namespace std; struct Node{int len,next,to;}edge[N*];
int head[N],num_edge;
int cnt[N],n,m,a,b,c,ml,md;
long long dis[N],ans;
bool used[N];
queue<int>q; void add(int u,int v,int l)
{
edge[++num_edge].to=v;
edge[num_edge].next=head[u];
edge[num_edge].len=l;
head[u]=num_edge;
} void SPFA(int s)
{
for (int i=; i<=n; ++i) dis[i]=INF,cnt[i]=;
q.push(s);
dis[s]=;
used[s]=true;
while (!q.empty())
{
int x=q.front(); q.pop();
for (int i=head[x]; i; i=edge[i].next)
if (dis[x]+edge[i].len<dis[edge[i].to])
{
dis[edge[i].to]=dis[x]+edge[i].len;
if (!used[edge[i].to])
{
q.push(edge[i].to);
cnt[edge[i].to]++;
if (cnt[edge[i].to]>=n){puts("-1");exit();}
used[edge[i].to]=true;
}
}
used[x]=false;
}
} int main()
{
scanf("%d%d%d",&n,&ml,&md);
for (int i=; i<=n; ++i) add(,i,);
for (int i=; i<=ml; ++i)
{
scanf("%d%d%d",&a,&b,&c);
add(a,b,c);
}
for (int i=; i<=md; ++i)
{
scanf("%d%d%d",&a,&b,&c);
add(b,a,-c);
}
SPFA(),SPFA();
if (dis[n]==INF) puts("-2");
else printf("%d\n",dis[n]);
}
BZOJ1731:[USACO]Layout 排队布局(差分约束)的更多相关文章
- 【BZOJ1731】[Usaco2005 dec]Layout 排队布局 差分约束
[BZOJ1731][Usaco2005 dec]Layout 排队布局 Description Like everyone else, cows like to stand close to the ...
- [Usaco2005 dec]Layout 排队布局 差分约束
填坑- 差分约束一般是搞一个不等式组,求xn-x1的最大最小值什么的,求最大值就转化成xa<=xb+w这样的,然后建图跑最短路(这才是最终约束的),举个例子 x1<=x0+2x2<= ...
- bzoj 1731: [Usaco2005 dec]Layout 排队布局 ——差分约束
Description 当排队等候喂食时,奶牛喜欢和它们的朋友站得靠近些.FJ有N(2<=N<=1000)头奶牛,编号从1到N,沿一条直线站着等候喂食.奶牛排在队伍中的顺序和它们的编号是相 ...
- bzoj 1731 [Usaco2005 dec]Layout 排队布局——差分约束
题目:https://www.lydsy.com/JudgeOnline/problem.php?id=1731 对差分约束理解更深.还发现美妙博客:http://www.cppblog.com/me ...
- bzoj 1731 Layout 排队布局 —— 差分约束
题目:https://www.lydsy.com/JudgeOnline/problem.php?id=1731 差分约束: ML: dis[y] - dis[x] <= k,即 x 向 y 连 ...
- 【bzoj1731】Layout 排队布局
1731: [Usaco2005 dec]Layout 排队布局 Time Limit: 5 Sec Memory Limit: 64 MBSubmit: 868 Solved: 495[Subm ...
- 1731: [Usaco2005 dec]Layout 排队布局*
1731: [Usaco2005 dec]Layout 排队布局 题意: n头奶牛在数轴上,不同奶牛可以在同个位置处,编号小的奶牛必须在前面.m条关系,一种是两头奶牛距离必须超过d,一种是两头奶牛距离 ...
- bzoj 1731: [Usaco2005 dec]Layout 排队布局【差分约束】
差分约束裸题,用了比较蠢的方法,先dfs_spfa判负环,再bfs_spfa跑最短路 注意到"奶牛排在队伍中的顺序和它们的编号是相同的",所以\( d_i-d_{i-1}>= ...
- POJ 3169 Layout (图论-差分约束)
Layout Time Limit: 1000MS Memory Limit: 65536K Total Submissions: 6574 Accepted: 3177 Descriptio ...
随机推荐
- Azure 应用服务中的 API 应用、ASP.NET 和 Swagger 入门
学习内容: 如何通过 Visual Studio 2015 中的内置工具在 Azure 应用服务中创建和部署 API 应用. 如何使用 Swashbuckle NuGet 包动态生成 Swagger ...
- 【C#】权限修饰符
这个看了蛮多遍的,但是由于有一些一直不用,老是忘记,记录一下:) private 成员只能由同一个类(class)类型中的其他成员访问. family 成员可由派生类访问,不管那些类型是否在用一个 ...
- WAMP配置httpd.conf允许外部访问
在电脑上开启Apache服务后,如何让外部网络访问呢? 在网上查找答案和问过一些小伙伴后,得到以以下方案.大致是在httpd.conf中加入一些语句以及利用自己的WiFi建立热点,让需要访问的设备连接 ...
- JSP简单实现登录和注销
JSP简单实现登录和注销 需求:用户登录成功后跳转到欢迎页面 用户登录失败跳转到初始的登录界面 用户点击注销,用户退出登录状态需要重新登录 登录页面的JSP代码: <%@ page langua ...
- 轻松学习java可重入锁(ReentrantLock)的实现原理(转 图解)
前言 相信学过java的人都知道 synchronized 这个关键词,也知道它用于控制多线程对并发资源的安全访问,兴许,你还用过Lock相关的功能,但你可能从来没有想过java中的锁底层的机制是怎么 ...
- 思维导图_Python_内置函数
- input textarea监听鼠标粘贴
发现一个问题,在input/textarea中如果是鼠标粘贴内容进去,发现判断不了value的改变,html代码如下: <!doctype html> <html> <h ...
- 多项式乘法,FFT与NTT
多项式: 多项式?不会 多项式加法: 同类项系数相加: 多项式乘法: A*B=C $A=a_0x^0+a_1x^1+a_2x^2+...+a_ix^i+...+a_{n-1}x^{n-1}$ $B=b ...
- sublime text 3中browsersync的使用
1.在项目所在位置右键选择Git Bash Here 2.输入 // --files 路径是相对于运行该命令的项目(目录) browser-sync start --server --files &q ...
- 解决servlet在web.xml中的路径跳转问题
<?xml version="1.0" encoding="UTF-8"?> <web-app version="3.0" ...