CCO '99 P1 - You Can't Get There From Here
View as PDFCanadian Computing Competition: 1999 Stage 2, Day 1, Problem 1
In a primitive video game, a spot bounces around within a rectangular grid. The southwest corner of the grid has coordinates  and the northeast corner has coordinates 
 where 
 and 
. The southeast corner has coordinates 
 and the northwest corner has coordinates 
. The spot always travels on the diagonal; that is, in one of the directions 
NE, NW, SE, SW. The outer edges of the grid serve as mirrors: after visiting a position on the edge of the grid the spot "bounces" off according to the normal rules of reflection (Snell's Law). For example, if the spot were travelling NE and hit the east edge of the grid, it would change direction to NW. If the spot were to hit the corner of the grid it would change to the opposite direction.
Given a grid size, two points  and 
 lying on the grid, and an initial direction, you are to determine if the spot moves from 
 to 
 and, if so, how far the spot moves (in terms of number of grid positions) before reaching 
 the first time.
Input Specification
The input consists of an integer , followed by 
 data sets. Each data set begins with a line containing 
 and 
, followed by two lines containing the coordinates of points 
 and 
 respectively, followed by one line containing 
NE, NW, SE, or SW - the initial direction of travel.
Output Specification
For each case, print a sentence as shown below indicating whether or not  can be reached, and, if it can, how far the spot moves before reaching 
.
Sample Input
2
3 4
0 0
0 4
NE
4 2
3 1
3 2
NW
Sample Output
B can be reached from A after 12 move(s).
B cannot be reached from A.
Comments