POJ-3169 Layout:http://poj.org/problem?id=3169 参考:https://blog.csdn.net/islittlehappy/article/details/81155802 题意: 一共有n头牛,有ml个关系好的牛的信息,有md个关系不好的牛的信息,对应输入的第一行的三个元素,接下来ml行,每行三个元素A,B,D,表示A牛和B牛相距不希望超过D,接下来md行,每行三个元素A,B,D表示A牛和B牛的相距至少要有D才行.求1号牛和n号牛的最大距离,如果…

http://poj.org/problem?id=3169 题意: 一堆牛在一条直线上按编号站队,在同一位置可以有多头牛并列站在一起,但编号小的牛所占的位置不能超过编号大的牛所占的位置,这里用d[i]表示编 号为i的牛所处的位置,即要满足d[i]-d[i+1]<=0,同时每两头牛之间有以下两种关系(对于输入的a b d来说):             1>如果是喜欢关系:即需要满足d[b]-d[a]<=d             2>如果是讨厌关系:即需要满足d[b]-a[a]&…

POJ3169 Layout 题意: n头牛编号为1到n,按照编号的顺序排成一列,每两头牛的之间的距离 >= 0.这些牛的距离存在着一些约束关系:1.有ml组(u, v, w)的约束关系,表示牛[u]和牛[v]之间的距离必须 <= w.2.有md组(u, v, w)的约束关系,表示牛[u]和牛[v]之间的距离必须 >= w.问如果这n头无法排成队伍,则输出-1,如果牛[1]和牛[n]的距离可以无限远,则输出-2,否则则输出牛[1]和牛[n]之间的最大距离. 分析: 记第i号牛的位置是d[…

描述 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…

题意:给定一些母牛,要求一个排列,有的母牛距离不能超过w,有的距离不能小于w,问你第一个和第n个最远距离是多少. 析:以前只是听说过个算法,从来没用过,差分约束. 对于第 i 个母牛和第 i+1 个,D[i] - D[i+1] <= 0,  D[j] -D[i ]<= k, D[i] - D[j] <= - k,那么这个题就可以用差分约束来求这个不等式组了. 1.对于差分不等式,a - b <= c ,建一条 b 到 a 的权值为 c 的边,求的是最短路,得到的是最大值(本题求的就…

题目链接:http://poj.org/problem?id=3169 很好的差分约束入门题目,自己刚看时学呢 代码: #include<iostream> #include<cstdio> #include<cstring> #include<cstdlib> #include<queue> using namespace std; #define INF 0x3f3f3f3f #define maxn 1010 int dis[maxn];…

Layout Time Limit: 1000MS   Memory Limit: 65536K Total Submissions: 6415   Accepted: 3098 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…

题目链接:http://poj.org/problem? id=3169 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 standin…

题意: 有N头牛, 有以下关系: (1)A牛与B牛相距不能大于k (2)A牛与B牛相距不能小于k (3)第i+1头牛必须在第i头牛前面 给出若干对关系(1),(2) 求出第N头牛与第一头牛的最长可能距离, 若无解输出-1, 若无限长输出-2 分析: 3个关系对应的 <= 式子是: dis[b] - dis[a] <= d(1) dis[a] - dis[b] <= -d(2) dis[i] - dis[i+1] <= -1(2) 目标式:dis[N] - dis[1] <=…

#define _CRT_SECURE_NO_WARNINGS /* 4 2 1 1 3 10 2 4 20 2 3 3 */ #include <iostream> #include <algorithm> #include <cstdio> #include <cstdlib> using namespace std; + ; ; //输入 int N, ML, MD; int AL[maxn], BL[maxn], DL[maxn]; int AD[m…

O - Layout(差分约束 + spfa) 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 the…

Layout   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…

Layout Time Limit: 1000MS   Memory Limit: 65536K Total Submissions: 15705   Accepted: 7551 题目链接:http://poj.org/problem?id=3169 Description: Like everyone else, cows like to stand close to their friends when queuing for feed. FJ has N (2 <= N <= 1,00…

题目:http://poj.org/problem?id=3169 题意:给你一组不等式了,求满足的最小解 分析: 裸裸的差分约束. 总结一下差分约束: 1.“求最大值”:写成"<=",求最短路 2.“求最小值”:写成">=",求最长路…

Layout Time Limit: 1000MS   Memory Limit: 65536K Total Submissions: 6574   Accepted: 3177 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…

题面 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…

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<=x0+7x3<=x0+8x2<=x1+3x3<=x2+2 那么解出来 x3<=x0+7x3<=x0+8x3<=x0+9 结果肯定是 x3<=x0+7 所以直接对于已知条件建边,大于小于可以互相转换,注意:相邻的要保证顺序. #include<cstdio>…

3169 -- Layout 继续差分约束. 这题要判起点终点是否连通,并且要判负环,所以要用到spfa. 对于ML的边,要求两者之间距离要小于给定值,于是构建(a)->(b)=c的边.同理,对于MD的,构建(b)->(a)=-c的边.然后就是(i+1)->(i)=0,两者距离大于0的限制. 代码如下: #include <cstdio> #include <iostream> #include <algorithm> #include <cst…

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 sin…

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 sin…

            布局 题目大意:有N头牛,编号1-N,按编号排成一排准备吃东西,有些牛的关系比较好,所以希望他们不超过一定的距离,也有一些牛的关系很不好,所以希望彼此之间要满足某个关系,牛可以挤在同一个位置上,现在给出N个牛的信息,问你能否实现一种排列方案,使得d[1]到d[N]最大?如果不存在输出-1,无限大输出-2 这一题看上去挺难的,但是如果你知道差分约束原理,这一题似乎还是挺简单的. 差分约束的原理是:存在任意线性方程,满足d[A]+c>=d[B],就可以表示为图的最短路形式,方…

题意:一个农夫有n头牛,他希望将这些牛按照编号 1-n排成一条直线,允许有几头牛站在同一点,但是必须按照顺序,有一些牛关系比较好,希望站的距离不超过某个值,而有一些牛关系不太好,所以希望站的距离大于等于某个值,问1号牛和n号牛之间的最远距离是多少. 差分约束的裸题,对于 d[v] - d[u] ≤ w 建立权值为 w 的单向边 e(u,v),对于 d[v] - d[u]  ≥ w 建立权值为 -w 的单向边 e(v,u),然后再根据牛必须按顺序排列建立权值为 0 的边 e(i+1,i),然后最短…

题目链接:http://poj.org/problem?id=3169 差分约束的解释:http://www.cnblogs.com/void/archive/2011/08/26/2153928.html 我也不是特别理解,要是给你a - b <= k 就建一条b->a权值为k的有向边,要是a - b >= k 就建一条a -> b边权是-k的有向边,要是让你求n到1的最大差,就是让你求1到n的最短距离. 差分约束系统有两种方式可以求解,最短路和最长路.当我们把不等式整理成d[a…

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 numbe…

<题目链接> 题目大意: 一些母牛按序号排成一条直线.有两种要求,A和B距离不得超过X,还有一种是C和D距离不得少于Y,问可能的最大距离.如果没有最大距离输出-1,如果1.n之间距离任意就输出-2,否则输出最大的距离. 解题分析:典型的差分约束,第一种约束,v-u<=c:第二种约束:v-u>=c  可以转化为 u-v<=c ,还有一种约束,因为题目要求按序号排序,所以 loc[i] - loc[i-1]>=0 ,即 loc[i-1]-loc[i]<=0 .以上就是…

题目链接http://poj.org/problem?id=3169 题目大意: 一些牛按序号排成一条直线. 有两种要求,A和B距离不得超过X,还有一种是C和D距离不得少于Y,问可能的最大距离.如果没有输出-1,如果可以随便排输出-2,否则输出最大的距离. 首先关于差分约束:https://blog.csdn.net/consciousman/article/details/53812818 了解了差分约束之后就知道该题典型的差分约束+spfa即可. #include<iostream> #i…

题意:有一串数字1~n,按顺序排序,给两种要求,一是给定u,v保证pos[v] - pos[u] <= w:二是给定u,v保证pos[v] - pos[u] >= w.求pos[n] - pos[1]最大,若无解输出-1,无穷多解输出-2. 思路:光看题目好像和最短路无关,其实这里用到了spfa的松弛操作来保证所给出的两种要求.若pos[v] - pos[u] >= w,则pos[v] +(- w) >=  pos[u],也就是pos[v] +(- w) < pos[u]时进…

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 numbe…

题目链接:http://poj.org/problem?id=3169 题目大意:n头牛,按编号1~n从左往右排列,可以多头牛站在同一个点,给出ml行条件,每行三个数a b c表示dis[b]-dis[a]<=c,接下来有md行条件,每行三个数a b c,表示dis[b]-dis[a]>=c.求出出第一头牛和第n头牛的最大可能距离.若不可能把所有牛排成一排即条件有矛盾,则输出“-1”,若第一头牛和第n头牛的距离可以无限大,则输出“-2”. 解题思路:第二道差分约束的题目.根据题目给出的三个约束…

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…