剛才.net課程期末考試,正好最後一題考的是遞迴實現fibonacci數列.順便就把**打出來發在這裡.
(雖然沒什麼技術含量 :wink: )
主要特性就是使用buffer將先前已經計算過的fibonacci數列的值儲存下來,減少遞迴時的重複計算開銷.c#沒直接的lazy evaluation,這種採取buffer的策略應該是不錯的選擇吧.
另外,實現了ienumerable和ienumerable介面,方便遍歷fibonacci物件當前已經快取了的值.
由於該數列採用[color=blue]int[/color]表示,在下標超過46(包括)時就會溢位,所以在檢查下標後會拋異常,使用時需要注意.
[code]using system;
using system.collections.generic;
namespace testfibonacci
// demostrate the implementation of indexer
for ( int i = 10; i < 46; i++ ) }}
///
/// a class that calculates the fibonacci sequence
/// and buffers previously calculated values.
/// the fibonacci sequence described here starts
/// from index 0 with a value of 1.
/// because the return value is represented in an int,
/// this class does not support indexes larger than 46.
///
public class fibonacci : ienumerator
///
/// create an fibonacci instance with specified buffer length.
///
///
public fibonacci( int initlength )
#endregion
#region fibonacci member methods
///
/// initialize the buffer of fibonacci sequence.
///
/// length of buffer.
/// cannot exceed 46 or an overflowexception will be thrown
public void initializebuffer( int length ) will cause int to overflow",
( length - 1 ).tostring( ) ) );
calculate( length - 1 );
}///
/// recursively calculate the fibonacci sequence.
///
///
///
private int calculate( int index )
return this.buffer[ index ];
}public ienumeratorgetenumerator( )
#endregion
#region fibonacci member properties
///
/// read-only property for retrieving the
/// fibonacci sequence at specified index.
///
///
///
public int this[ int index ]
}#endregion
#region fibonacci member fields
///
/// buffers previously calculated values.
///
private listbuffer;
#endregion
#region ienumeratormembers
///
/// current enumerator cursor position.
///
private int position = -1;
public int current catch ( indexoutofrangeexception ) }}
#endregion
#region idisposable members
public void dispose( )
#endregion
#region ienumerator members
object system.collections.ienumerator.current
}public bool movenext( )
public void reset( )
#endregion}}
[/code]
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