Part Acquisition POJ - 2457 （Spfa+优先队列优化+输出路径）

最新推荐文章于 2021-07-13 10:44:03 发布

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最新推荐文章于 2021-07-13 10:44:03 发布

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分类专栏：最短路文章标签： acm 最短路

本文链接：https://blog.youkuaiyun.com/weixin_41190227/article/details/90181594

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这篇博客介绍了ACM竞赛中的一道问题，即如何在星际旅行中通过物物交换从地球获取新的挤奶机。问题转化为寻找最短路径的图论问题，使用SPFA（Shortest Path Faster Algorithm）配合优先队列优化来解决。如果无法获取目标物品，输出-1。博客提供了样例输入和输出，并解释了解题思路，将商品和交易方式抽象为节点和边，通过求解最短路径来确定最小交易次数和路径。

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The cows have been sent on a mission through space to acquire a new milking machine for their barn. They are flying through a cluster of stars containing N (1 <= N <= 50,000) planets, each with a trading post.

The cows have determined which of K (1 <= K <= 1,000) types of objects (numbered 1..K) each planet in the cluster desires, and which products they have to trade. No planet has developed currency, so they work under the barter system: all trades consist of each party trading exactly one object (presumably of different types).

The cows start from Earth with a canister of high quality hay (item 1), and they desire a new milking machine (item K). Help them find the best way to make a series of trades at the planets in the cluster to get item K. If this task is impossible, output -1.

Input

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

* Lines 2..N+1: Line i+1 contains two

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