Google中国挑战赛2005 250分题 (2)

这是9号房间的250分题：

Problem Statement
    
You are given a String[] cityMap representing the layout of a city. The city consists of blocks. The first element of cityMap represents the first row of blocks, etc. A 'B' character indicates a location where there is a bus stop. There will be exactly one 'X' character, indicating your location. All other characters will be '.'. You are also given an int walkingDistance, which is the maximum distance you are willing to walk to a bus stop. The distance should be calculated as the number of blocks vertically plus the number of blocks horizontally. Return the number of bus stops that are within walking distance of your current location.
Definition
    
Class:
BusStops
Method:
countStops
Parameters:
String[], int
Returns:
int
Method signature:
int countStops(String[] cityMap, int walkingDistance)
(be sure your method is public)
    

Constraints
-
cityMap will contain between 1 and 50 elements, inclusive.
-
Each element of cityMap will contain between 1 and 50 characters, inclusive.
-
Each element of cityMap will contain the same number of characters.
-
Each character of each element of cityMap will be 'B', 'X', or '.'.
-
There will be exactly one 'X' character in cityMap.
-
walkingDistance will be between 1 and 100, inclusive.
Examples
0)

    
{"...B.",
 ".....",
 "..X.B",
 ".....",
 "B...."}
3
Returns: 2
You can reach the bus stop at the top (3 units away), or on the right (2 units away). The one in the lower left is 4 units away, which is too far.
1)

    
{"B.B..",
 ".....",
 "B....",
 ".....",
 "....X"}
8
Returns: 3
A distance of 8 can get us anywhere on the map, so we can reach all 3 bus stops.
2)

    
{"BBBBB",
 "BB.BB",
 "B.X.B",
 "BB.BB",
 "BBBBB"}
1
Returns: 0
Plenty of bus stops, but unfortunately we cannot reach any of them.
3)

    
{"B..B..",
 ".B...B",
 "..B...",
 "..B.X.",
 "B.B.B.",
 ".B.B.B"}
3
Returns: 7

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