4790：[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.

5 6
###=##
#.W.##
#.####
#.@W##
######

3

提示

Sample Explanation: ```plain ###=## #.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. 标签: P1825|模拟|搜索|2011|USACO|广度优先搜索 BFS|最短路

来源

P1825|[USACO11OPEN] Corn Maze S