#P1825. [USACO11OPEN] Corn Maze S
[USACO11OPEN] Corn Maze S
题目描述
This past fall, Farmer John took the cows to visit a corn maze. But this wasn't just any corn maze: it featured several gravity-powered teleporter slides, which cause cows to teleport instantly from one point in the maze to another. The slides work in both directions: a cow can slide from the slide's start to the end instantly, or from the end to the start. If a cow steps on a space that hosts either end of a slide, she must use the slide.
The outside of the corn maze is entirely corn except for a single exit.
The maze can be represented by an N x M (2 <= N <= 300; 2 <= M <= 300) grid. Each grid element contains one of these items:
* Corn (corn grid elements are impassable)
* Grass (easy to pass through!)
* A slide endpoint (which will transport a cow to the other endpoint)
* The exit
A cow can only move from one space to the next if they are adjacent and neither contains corn. Each grassy space has four potential neighbors to which a cow can travel. It takes 1 unit of time to move from a grassy space to an adjacent space; it takes 0 units of time to move from one slide endpoint to the other.
Corn-filled spaces are denoted with an octothorpe (#). Grassy spaces are denoted with a period (.). Pairs of slide endpoints are denoted with the same uppercase letter (A-Z), and no two different slides have endpoints denoted with the same letter. The exit is denoted with the equals sign (=).
Bessie got lost. She knows where she is on the grid, and marked her current grassy space with the 'at' symbol (@). What is the minimum time she needs to move to the exit space?
输入格式
Line 1: Two space separated integers: N and M
Lines 2..N+1: Line i+1 describes row i of the maze: M characters (no spaces)
输出格式
Line 1: An integer, corresponding to the shortest time that Bessie needs to exit the maze.
题目大意
奶牛们去一个 玉米迷宫,。
迷宫里有一些传送装置,可以将奶牛从一点到另一点进行瞬间转移。这些装置可以双向使用。
如果一头奶牛处在这个装置的起点或者终点,这头奶牛就必须使用这个装置,奶牛在传送过后不会立刻进行第二次传送,即不会卡在传送装置的起点和终点之间来回传送。
玉米迷宫除了唯一的一个出口都被玉米包围。
迷宫中的每个元素都由以下项目中的一项组成:
- 玉米,
#
表示,这些格子是不可以通过的。 - 草地,
.
表示,可以简单的通过。 - 传送装置,每一对大写字母 到 表示。
- 出口,
=
表示。 - 起点,
@
表示
奶牛能在一格草地上可能存在的四个相邻的格子移动,花费 个单位时间。从装置的一个结点到另一个结点不花时间。
5 6
###=##
#.W.##
#.####
#.@W##
######
3
提示
Sample Explanation:
###=##
#.W.##
#.####
#.@W##
######
The endpoints of the only slide are marked with capital letters W.
The optimal strategy (which takes 3 units of time) is to: Move right to the slide endpoint using 1 unit of time, transport to the other endpoint using 0 units of time, move right using 1 unit of time, and move up to the exit using 1 unit of time.
Related
In following homework: