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];…

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…

思路: 差分约束,难在建图.(我是不会告诉你我刚学会SPFA的...) 把每个区间的ai–>bi连一条长度为ci的边. k–>k+1连一条长度为0的边. k+1–>k连一条长度为-1的边. 求最长路即可. // by SiriusRen #include <queue> #include <cstdio> #include <algorithm> #define N 55555 using namespace std; int w[N*3],v[N*3…

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…

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…

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…

题目链接:http://poj.org/problem?id=3169 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…

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…

POJ 1364 题解:最短路式子:d[v]<=d[u]+w 式子1:sum[a+b+1]−sum[a]>c      —      sum[a]<=sum[a+b+1]−c−1       —      (a+b+1,a) −c−1 式子2:sum[a+b+1]−sum[a]<c      —      sum[a+b+1]<=sum[a]+c−1       —      (a,a+b+1)  c−1 注意:先移项,移项完后再处理没有等于的情况. 附加式:sum[0]&l…

题目链接:http://poj.org/problem?id=3159 题目大意:给n个人派糖果,给出m组数据,每组数据包含A,B,C三个数,意思是A的糖果数比B少的个数不多于C,即B的糖果数 - A的糖果数<=C . 最后求n 比 1 最多多多少颗糖果. 解题思路:经典差分约束的题目,具体证明看这里<数与图的完美结合——浅析差分约束系统>. 不妨将糖果数当作距离,把相差的最大糖果数看成有向边AB的权值,我们得到 dis[B]-dis[A]<=w(A,B).看到这里,我们可以联想到…