2019焦作F 以及图论题时限内存经验

最新推荐文章于 2022-07-23 09:55:40 发布

转载最新推荐文章于 2022-07-23 09:55:40 发布 · 225 阅读

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原文链接：http://www.cnblogs.com/youchandaisuki/p/10891364.html

本文介绍了一个基于六边形网格的迷宫路径搜索问题，重点在于如何优化搜索算法的时间和空间复杂度，包括使用不同的输入读取方法对性能的影响，以及如何避免因大量数据处理而导致的内存溢出。

http://codeforces.com/gym/102028/problem/F

A honeycomb is a mass wax cells built by honey bees, which can be described as a regular tiling of the Euclidean plane, in which three hexagons meet at each internal vertex. The internal angle of a hexagon is

$\text{[math]}$

Here we guarantee that the first cell in the second column always locates in the bottom right side of the first cell in the first column, as shown above. A general honeycomb may, on the basis of a complete honeycomb, lose some walls between adjacent cells, but the honeycomb is still in a closed form. A possible case looks like the figure below.

$\text{[math]}$

Hamilton is a brave bee living in a general honeycomb. Now he wants to move from a starting point to a specified destination. The image below gives a feasible path in a

$\text{[math]}$

Please help him find the minimum number of cells that a feasible path has to pass through (including the starting point and the destination) from the specified starting point to the destination.

Input

The input contains several test cases, and the first line contains a positive integer

For each test case, the first line contains two integers

The following

We guarantee that all outermost wall exist so that the given honeycomb is closed, and exactly one "S" and one "T" appear in the given honeycomb. Besides, the sum of

Output

For each test case, output a line containing the minimum number of cells that Hamilton has to visit moving from the starting cell ("S") to the destination ("T"), including the starting cell and the destination. If no feasible path exists, output -1 instead.

Example

input

Copy

1
3 4
  +---+       +---+
 /     \     /     \
+       +---+       +---+
 \           \     /     \
  +   +   S   +---+   T   +
 /     \     /           /
+       +---+       +   +
 \           \     /     \
  +---+       +---+       +
 /                       /
+       +---+       +   +
 \                 /     \
  +---+       +---+       +
       \     /     \     /
        +---+       +---+

output

Copy

题意就是走六边形迷宫。

其实很简单一个题目，只是题面和样例看起来很吓人...bfs随便搞搞就有思路了，但是这个题目难度不在这里。而是大矩阵的图导致的各种时间和空间开销上的问题。

1.从时间上看，getchar()一个一个取是最快的（374ms），其次是gets()(607ms)，最慢的是cin.getline()，第三个在本题直接导致tle。（下图时间从小到大为方法从左到右）

2.从空间上看，对于大的矩阵图，vis、mp等数组一定要开到全局，不然会爆栈，如果调试爆栈，把数组开到全局试试。

3.memset初始化并没有两层for快，本题memset会tle。

转载于:https://www.cnblogs.com/youchandaisuki/p/10891364.html