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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"> <html> <head> <title>page_656</title> <link rel="stylesheet" href="reset.css" type="text/css" media="all"> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> </head> <body> <table summary="top nav" border="0" width="100%"> <tr> <td align="left" width="30%" style="background: #EEF3E2"><a style="color: blue; font-size: 120%; font-weight: bold; text-decoration: none; font-family: verdana;" href="page_655.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_656</strong></td> <td align="right" width="30%" style="background: #EEF3E2"><a style="color: blue; font-size: 120%; font-weight: bold; text-decoration: none; font-family: verdana;" href="page_657.html">next page ></a></td> </tr> <tr> <td align="left" colspan="3" style="background: #ffffff; padding: 20px;"> <table border="0" width="100%" cellpadding="0"><tr><td align="center"> <table border="0" cellpadding="2" cellspacing="0" width="100%"><tr><td align="left"></td> <td align="right"></td> </tr></table></td></tr><tr><td align="left"><p></p><table border="0" cellspacing="0" cellpadding="0" width="100%"><tr><td align="right"><font face="Times New Roman, Times, Serif" size="2" color="#FF0000">Page 656</font></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Courier New, Courier, Mono New, Courier, Mono" size="2">聽聽聽聽int聽聽聽聽聽聽placeCount;聽聽聽聽聽聽聽聽聽//聽Loop聽control聽variable<br />聽聽聽聽int聽聽聽聽聽聽minIndex;聽聽聽聽聽聽聽聽聽聽聽//聽Index聽of聽minimum聽so聽far<br /><br />聽聽聽聽for聽(passCount聽=聽0;聽passCount聽<聽length聽-聽1;聽passCount++)<br />聽聽聽聽{<br />聽聽聽聽聽聽聽聽聽聽//聽Invariant聽(prior聽to聽test):<br />聽聽聽聽聽聽聽聽聽聽//聽聽聽聽聽list[0..passCount-1]聽are聽in聽ascending聽order<br />聽聽聽聽聽聽聽聽聽聽//聽聽聽聽聽聽聽and聽contain聽the聽passCount聽smallest聽items<br />聽聽聽聽聽聽聽聽聽聽//聽聽&&聽0聽<=聽passCount聽<=聽length聽-聽1<br /><br />聽聽聽聽聽聽聽minIndex聽=聽passCount;<br /><br />聽聽聽聽聽聽聽//聽Find聽the聽index聽of聽the聽smallest聽component<br />聽聽聽聽聽聽聽//聽in聽list[passCount..length-1]<br /><br />聽聽聽聽聽聽聽for聽(placeCount聽=聽passCount聽+聽1;聽placeCount聽<聽length;<br />聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽聽placeCount++)<br /><br />聽聽聽聽聽聽聽聽聽聽聽聽//聽Invariant聽(prior聽to聽test):<br />聽聽聽聽聽聽聽聽聽聽聽聽//聽聽聽聽list[minIndex]聽<=聽all聽list[passCount..placeCount-1]<br />聽聽聽聽聽聽聽聽聽聽聽聽//聽&&聽placeCount聽<=聽length<br /><br />聽聽聽聽聽聽聽聽聽聽if聽(list[placeCount]聽<聽list[minIndex])<br />聽聽聽聽聽聽聽聽聽聽聽聽聽minIndex聽=聽placeCount;<br /><br />聽聽聽聽聽聽聽//聽Swap聽list[minIndex]聽and聽list[passCount]<br /><br />聽聽聽聽聽聽聽temp聽=聽list[minIndex];<br />聽聽聽聽聽聽聽list[minIndex]聽=聽list[passCount];<br />聽聽聽聽聽聽聽list[passCount]聽=聽temp;<br />聽聽聽聽}<br />}</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3">Note that with each pass through the inner loop, we are looking for the minimum value in the rest of the list (</font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">list[passCount]</font><font face="Times New Roman, Times, Serif" size="3"> through </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">list[length-1]</font><font face="Times New Roman, Times, Serif" size="3">). Therefore, </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">minIndex</font><font face="Times New Roman, Times, Serif" size="3"> is initialized to </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">passCount</font><font face="Times New Roman, Times, Serif" size="3"> and the inner loop runs from </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">placeCount</font><font face="Times New Roman, Times, Serif" size="3"> equal to </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">passCount+1</font><font face="Times New Roman, Times, Serif" size="3"> through </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">length-1</font><font face="Times New Roman, Times, Serif" size="3">.</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3">Note also that we may swap a component with itself, which occurs if no value in the remaining list is smaller than </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">list[passCount]</font><font face="Times New Roman, Times, Serif" size="3">. We could avoid such an unnecessary swap by checking to see if </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">minIndex</font><font face="Times New Roman, Times, Serif" size="3"> is equal to </font><font face="Courier New, Courier, Mono New, Courier, Mono" size="3">passCount</font><font face="Times New Roman, Times, Serif" size="3">. Because this comparison would have to be made during each iteration of the loop, it is more efficient not to check for this possibility and just to swap something with itself occasionally. If the components we are sorting are much more complex than simple numbers, we might reconsider this decision.</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3">This algorithm sorts the components into ascending order. To sort them into descending order, we need to scan for the maximum value instead of</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table></td></tr></table><p><font size="0"></font></p>聽 </td> </tr> <tr> <td align="left" width="30%" style="background: #EEF3E2"><a style="color: blue; font-size: 120%; font-weight: bold; text-decoration: none; font-family: verdana;" href="page_655.html">< previous page</a></td> <td align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_656</strong></td> <td align="right" width="30%" style="background: #EEF3E2"><a style="color: blue; font-size: 120%; font-weight: bold; text-decoration: none; font-family: verdana;" href="page_657.html">next page ></a></td> </tr> </table> </body> </html>⌨️ 快捷键说明
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