RECURSION - Introduction to Java Programming: Comprehensive Version - page 733

The program enables the user to place or remove a mark on a cell. A path
consists of adjacent unmarked cells. Two cells are said to be adjacent if they
are horizontal or vertical neighbors, but not if they are diagonal neighbors.

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The path does not contain cells that form a square. The path in Figure 18.13b,
for example, does not meet this condition. (The condition makes a path easy
to identify on the board.)

■

**18.27

( Koch snowflake fractal ) The text presented the Sierpinski triangle fractal. In
this exercise, you will write a program to display another fractal, called the Koch
snowflake , named after a famous Swedish mathematician. A Koch snowflake is
created as follows:
1. Begin with an equilateral triangle, which is considered to be the Koch fractal
of order (or level) 0 , as shown in Figure 18.14a.
2. Divide each line in the shape into three equal line segments and draw an out-
ward equilateral triangle with the middle line segment as the base to create a
Koch fractal of order 1 , as shown in Figure 18.14b.
3. Repeat Step 2 to create a Koch fractal of order 2 , 3 , . . . , and so on, as shown
in Figure 18.14c-d.

(a) (b) (c) (d)

F IGURE 18.14

A Koch snowflake is a fractal starting with a triangle.

**18.28

( Nonrecursive directory size ) Rewrite Listing 18.7, DirectorySize.java, without
using recursion.

*18.29

( Number of files in a directory ) Write a program that prompts the user to enter a
directory and displays the number of the files in the directory.

**18.30

( Find words ) Write a program that finds all occurrences of a word in all the files
under a directory, recursively. Pass the parameters from the command line as
follows:

VideoNote

Search a string in a directory

java Exercise18_30 dirName word

**18.31

( Replace words ) Write a program that replaces all occurrences of a word with a
new word in all the files under a directory, recursively. Pass the parameters from
the command line as follows:

java Exercise18_31 dirName oldWord newWord

***18.32

( Game: Knight's Tour ) The Knight's Tour is an ancient puzzle. The objective is
to move a knight, starting from any square on a chessboard, to every other square
once, as shown in Figure 18.15a. Note that the knight makes only L-shaped
moves (two spaces in one direction and one space in a perpendicular direc-
tion). As shown in Figure 18.15b, the knight can move to eight squares. Write