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<HTML><HEAD><TITLE>Finding Items in a List</TITLE></HEAD><BODY bgcolor="#FFFFFF"> <a href="../index.html" target="_top"><img src="../icons/usins.gif" alt="Logo" align=right></a><b>Data Structures and Algorithms with Object-Oriented Design Patterns in Python</b><br><A NAME="tex2html3307" HREF="page183.html"><IMG WIDTH=37 HEIGHT=24 ALIGN=BOTTOM ALT="next" SRC="../icons/next_motif.gif"></A> <A NAME="tex2html3305" HREF="page179.html"><IMG WIDTH=26 HEIGHT=24 ALIGN=BOTTOM ALT="up" SRC="../icons/up_motif.gif"></A> <A NAME="tex2html3299" HREF="page181.html"><IMG WIDTH=63 HEIGHT=24 ALIGN=BOTTOM ALT="previous" SRC="../icons/previous_motif.gif"></A> <A NAME="tex2html3309" HREF="page611.html"><IMG WIDTH=43 HEIGHT=24 ALIGN=BOTTOM ALT="index" SRC="../icons/index_motif.gif"></A> <BR><HR><H3><A NAME="SECTION007123000000000000000">Finding Items in a List</A></H3><P>Program <A HREF="page182.html#progorderedListAsLinkedListc"><IMG ALIGN=BOTTOM ALT="gif" SRC="../icons/cross_ref_motif.gif"></A> defines the <tt>__contains__</tt>and <tt>find</tt> methods of the <tt>ListAsLinkedList</tt> class.The implementations of these methods are almost identical.However, they differ in two key aspects--the comparison used and the return value.<P><P><A NAME="9887"> </A><A NAME="progorderedListAsLinkedListc"> </A> <IMG WIDTH=575 HEIGHT=390 ALIGN=BOTTOM ALT="program9420" SRC="img754.gif" ><BR><STRONG>Program:</STRONG> <tt>OrderedListAsLinkedList</tt> class <tt>__contains__</tt> and <tt>find</tt> methods.<BR><P><P>The <tt>__contains__</tt> method tests whethera particular object instance is contained in the ordered list.It returns a <tt>bool</tt> value indicating whether the object is present.The running time of this method is clearly <I>O</I>(<I>n</I>),where <IMG WIDTH=72 HEIGHT=9 ALIGN=BOTTOM ALT="tex2html_wrap_inline60691" SRC="img663.gif" >,the number of items in the ordered list.<P>The <tt>find</tt> method locates an objectwhich matches a given object.The match is determined by using the <tt>==</tt> operator.<tt>find</tt> returns a reference to the matching object if one is found.Otherwise, it returns <tt>None</tt>.The running time for this method,is <IMG WIDTH=136 HEIGHT=24 ALIGN=MIDDLE ALT="tex2html_wrap_inline61009" SRC="img738.gif" >,where <IMG WIDTH=53 HEIGHT=24 ALIGN=MIDDLE ALT="tex2html_wrap_inline61007" SRC="img737.gif" > is the time required to do the comparison,and <IMG WIDTH=78 HEIGHT=9 ALIGN=BOTTOM ALT="tex2html_wrap_inline61037" SRC="img743.gif" > is the number of items in the ordered list.This simplifies to <I>O</I>(<I>n</I>) when the comparison can be done in constant time.<P><HR><A NAME="tex2html3307" HREF="page183.html"><IMG WIDTH=37 HEIGHT=24 ALIGN=BOTTOM ALT="next" SRC="../icons/next_motif.gif"></A> <A NAME="tex2html3305" HREF="page179.html"><IMG WIDTH=26 HEIGHT=24 ALIGN=BOTTOM ALT="up" SRC="../icons/up_motif.gif"></A> <A NAME="tex2html3299" HREF="page181.html"><IMG WIDTH=63 HEIGHT=24 ALIGN=BOTTOM ALT="previous" SRC="../icons/previous_motif.gif"></A> <A NAME="tex2html3309" HREF="page611.html"><IMG WIDTH=43 HEIGHT=24 ALIGN=BOTTOM ALT="index" SRC="../icons/index_motif.gif"></A> <P><ADDRESS><img src="../icons/bruno.gif" alt="Bruno" align=right><a href="../copyright.html">Copyright © 2003</a> by <a href="../signature.html">Bruno R. Preiss, P.Eng.</a> All rights reserved.</ADDRESS></BODY></HTML>⌨️ 快捷键说明
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