Life is a journey, and the road we travel has twists and turns, which sometimes lead us to unexpected places and unexpected people. Now our journey of Dalian ends. To be carefully considered are the following questions. Next month in Xian, an essenti…

2017 ACM-ICPC 亚洲区(乌鲁木齐赛区)网络赛Our Journey of Dalian Ends 题意:要求先从大连到上海,再从上海打西安,中途会经过其他城市,每个城市只能去一次,出一次,给出航班信息,问最小花费. 每个城市只能去一次,出一次,那么很明显需要对每个城市拆点,就分成入点和出点,然后如果按照题意说法,把汇点连大连和上海,然后把上海和西安连汇点,那么很明显不对, 因为跑出来的可能是从上海直接到的上海,然后大连到西安,所以不能把跟汇点和源点相连的设在同一点,那么我们就可以汇点…

题目链接 题意 : 给出一副图,大连是起点,终点是西安,要求你求出从起点到终点且经过中转点上海的最小花费是多少? 分析 : 最短路是最小费用最大流的一个特例,所以有些包含中转限制或者经过点次数有限制的最短路问题都可以考虑使用最小费用最大流来建图解决. 首先对于每个点都只能经过一次这个限制,在网络流中是比较常见的一个限制,只要将所有的点由一拆二且两点间连容量为 1 且花费为 0 的边. 这题的建图很巧妙,是将中转点作为汇点,提示到了这里不如停下来想想如何建图? 然后抽象出一个超级源点,然后将起点和…

题目描述: Life is a journey, and the road we travel has twists and turns, which sometimes lead us to unexpected places and unexpected people. Now our journey of Dalian ends. To be carefully considered are the following questions. Next month in Xian, an e…

Our Journey of Xian Ends https://nanti.jisuanke.com/t/18521 262144K   Life is a journey, and the road we travel has twists and turns, which sometimes lead us to unexpected places and unexpected people. Now our journey of Xian ends. To be carefully co…

Farm Tour Time Limit: 1000ms Memory Limit: 65536KB This problem will be judged on PKU. Original ID: 2135 64-bit integer IO format: %lld      Java class name: Main   When FJ's friends visit him on the farm, he likes to show them around. His farm compr…

描述 When FJ's friends visit him on the farm, he likes to show them around. His farm comprises N (1 <= N <= 1000) fields numbered 1..N, the first of which contains his house and the Nth of which contains the big barn. A total M (1 <= M <= 10000)…

POJ 2135 Farm Tour (网络流,最小费用最大流) Description When FJ's friends visit him on the farm, he likes to show them around. His farm comprises N (1 <= N <= 1000) fields numbered 1..N, the first of which contains his house and the Nth of which contains the b…

图论 网络流 最大流 INF(初始值) 路径上权值最小的边,决定流量大小. 流量网络的三个特性: ①流量控制 ②反对称性 ③流量守恒 残余网络:保留了c(e)容量<f(e)流量[可以继续流,因为还有f(e)-c(e)的流量]和 c(e)>0的反向边[可以回退]. 增广路定理:网络中达到最大流当且仅当残余网络中不存在增广路. 所以总结做题方法就是不断找增广路,有三种方法: ①Ford-Fvkerson(DFS) 伪代码: 不断地在残余网络中找增广路伪代码: FF{ flow=0; while(t…

Description When FJ's friends visit him on the farm, he likes to show them around. His farm comprises N (1 <= N <= 1000) fields numbered 1..N, the first of which contains his house and the Nth of which contains the big barn. A total M (1 <= M <…