【POJ 2135 Farm Tour】

题目链接

http://poj.org/problem?id=2135

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 <= 10000) paths that connect the fields in various ways. Each path connects two different fields and has a nonzero length smaller than 35,000.

To show off his farm in the best way, he walks a tour that starts at his house, potentially travels through some fields, and ends at the barn. Later, he returns (potentially through some fields) back to his house again.

He wants his tour to be as short as possible, however he doesn’t want to walk on any given path more than once. Calculate the shortest tour possible. FJ is sure that some tour exists for any given farm.

Input

* Line 1: Two space-separated integers: N and M.

* Lines 2..M+1: Three space-separated integers that define a path: The starting field, the end field, and the path’s length.

Output

A single line containing the length of the shortest tour.

Sample Input

4 5
1 2 1
2 3 1
3 4 1
1 3 2
2 4 2

Sample Output

6

建一个超级源点\(0\)和超级汇点\(N+1\),\(0\)到\(1\)建一条容量2费用1的边,\(N\)到\(N+1\)建一条容量2费用1的边,其余两点\((x,y)\)建四条边,分别为\(x\)到\(y\)的正向边和反向边、\(y\)到\(x\)的正向边和反向边,然后跑一遍最小费用最大流就行了。

 

stdKonjac

stdKonjac

一只挣扎的蒟蒻ACMer

评论太激烈有些评论需要亲动动手指翻页

留下你的评论

*评论支持代码高亮<pre class="prettyprint linenums">代码</pre>

*