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<html xmlns:o="urn:schemas-microsoft-com:office:office"xmlns:w="urn:schemas-microsoft-com:office:word"xmlns="http://www.w3.org/TR/REC-html40"><head><meta http-equiv=Content-Type content="text/html; charset=GB2312"><meta name=ProgId content=Word.Document><meta name=Generator content="Microsoft Word 9"><meta name=Originator content="Microsoft Word 9"><link rel=File-List href="./No44.files/filelist.xml"><title>回溯</title><!--[if gte mso 9]><xml> <o:DocumentProperties> <o:Author>lixuewu</o:Author> <o:LastAuthor>a</o:LastAuthor> <o:Revision>2</o:Revision> <o:TotalTime>1</o:TotalTime> <o:Created>1996-12-31T16:40:00Z</o:Created> <o:LastSaved>1996-12-31T16:40:00Z</o:LastSaved> <o:Pages>5</o:Pages> <o:Words>4038</o:Words> <o:Characters>23021</o:Characters> <o:Company>dksl</o:Company> <o:Lines>191</o:Lines> <o:Paragraphs>46</o:Paragraphs> <o:CharactersWithSpaces>28271</o:CharactersWithSpaces> <o:Version>9.2812</o:Version> </o:DocumentProperties></xml><![endif]--><!--[if gte mso 9]><xml> <w:WordDocument> <w:PunctuationKerning/> <w:DrawingGridHorizontalSpacing>5.25 磅</w:DrawingGridHorizontalSpacing> <w:DrawingGridVerticalSpacing>7.8 磅</w:DrawingGridVerticalSpacing> <w:DisplayHorizontalDrawingGridEvery>0</w:DisplayHorizontalDrawingGridEvery> <w:DisplayVerticalDrawingGridEvery>2</w:DisplayVerticalDrawingGridEvery> <w:Compatibility> <w:SpaceForUL/> <w:BalanceSingleByteDoubleByteWidth/> <w:DoNotLeaveBackslashAlone/> <w:ULTrailSpace/> <w:DoNotExpandShiftReturn/> <w:AdjustLineHeightInTable/> <w:UseFELayout/> </w:Compatibility> </w:WordDocument></xml><![endif]--><style><!-- /* Font Definitions */@font-face {font-family:宋体; panose-1:2 1 6 0 3 1 1 1 1 1; mso-font-alt:SimSun; mso-font-charset:134; mso-generic-font-family:auto; mso-font-pitch:variable; mso-font-signature:3 135135232 16 0 262145 0;}@font-face {font-family:仿宋_GB2312; panose-1:2 1 6 9 3 1 1 1 1 1; mso-font-charset:134; mso-generic-font-family:modern; mso-font-pitch:fixed; mso-font-signature:1 135135232 16 0 262144 0;}@font-face {font-family:"\@仿宋_GB2312"; panose-1:2 1 6 9 3 1 1 1 1 1; mso-font-charset:134; mso-generic-font-family:modern; mso-font-pitch:fixed; mso-font-signature:1 135135232 16 0 262144 0;}@font-face {font-family:"\@宋体"; panose-1:2 1 6 0 3 1 1 1 1 1; mso-font-charset:134; mso-generic-font-family:auto; mso-font-pitch:variable; mso-font-signature:1 135135232 16 0 262144 0;} /* Style Definitions */p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; text-align:justify; text-justify:inter-ideograph; mso-pagination:none; font-size:10.5pt; mso-bidi-font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:宋体; mso-font-kerning:1.0pt;}p.MsoFooter, li.MsoFooter, div.MsoFooter {margin:0cm; margin-bottom:.0001pt; mso-pagination:none; tab-stops:center 207.65pt right 415.3pt; layout-grid-mode:char; font-size:9.0pt; font-family:"Times New Roman"; mso-fareast-font-family:宋体; mso-font-kerning:1.0pt;} /* Page Definitions */@page {mso-page-border-surround-header:no; mso-page-border-surround-footer:no; mso-gutter-position:top;}@page Section1 {size:515.95pt 728.6pt; margin:72.0pt 2.0cm 62.35pt 2.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-even-footer:url("./No44.files/header.htm") ef1; mso-footer:url("./No44.files/header.htm") f1; mso-paper-source:0;}div.Section1 {page:Section1;}--></style></head><body lang=ZH-CN style='tab-interval:21.0pt;text-justify-trim:punctuation' bgcolor="#e8ffe8"><div class=Section1><p class=MsoNormal align=left style='text-align:left;text-indent:112.0pt;mso-char-indent-count:7.0;mso-char-indent-size:16.0pt;mso-layout-grid-align:none;text-autospace:none'><span style='font-size:16.0pt;font-family:仿宋_GB2312;color:blue;mso-font-kerning:0pt'>第<span lang=EN-US> 4 章<spanstyle="mso-spacerun: yes"> </span>回溯<o:p></o:p></span></span></p><p class=MsoNormal align=left style='text-align:left;mso-layout-grid-align:none;text-autospace:none'><span lang=EN-US style='font-size:16.0pt;font-family:仿宋_GB2312;color:blue;mso-font-kerning:0pt'><![if !supportEmptyParas]> <![endif]><o:p></o:p></span></p><p class=MsoNormal align=left style='text-align:left;text-indent:20.0pt;mso-char-indent-count:2.0;mso-char-indent-size:10.0pt;mso-layout-grid-align:none;text-autospace:none'><span style='font-size:10.0pt;font-family:仿宋_GB2312;color:black;mso-font-kerning:0pt'>寻找问题的解的一种可靠的方法是首先列出所有候选解，然后依次检查每一个，在检查完所有或部分候选解后，即可找到所需要的解。理论上，当候选解数量有限并且通过检查所有或部分候选解能够得到所需解时，上述方法是可行的。不过，在实际应用中，很少使用这种方法，因为候选解的数量通常都非常大（比如指数级，甚至是大数阶乘），即便采用最快的计算机也只能解决规模很小的问题。对候选解进行系统检查的方法有多种，其中回溯和分枝定界法是比较常用的两种方法。按照这两种方法对候选解进行系统检查通常会使问题的求解时间大大减少（无论对于最坏情形还是对于一般情形）。事实上，这些方法可以使我们避免对很大的候选解集合进行检查，同时能够保证算法运行结束时可以找到所需要的解。因此，这些方法通常能够用来求解规模很大的问题。<spanlang=EN-US><o:p></o:p></span></span></p><p class=MsoNormal align=left style='text-align:left;text-indent:20.0pt;mso-char-indent-count:2.0;mso-char-indent-size:10.0pt;mso-layout-grid-align:none;text-autospace:none'><span style='font-size:10.0pt;font-family:仿宋_GB2312;color:black;mso-font-kerning:0pt'>本章集中阐述回溯方法，这种方法被用来设计货箱装船、背包、最大完备子图、旅行商和电路板排列问题的求解算法。<spanlang=EN-US><o:p></o:p></span></span></p><p class=MsoNormal align=left style='text-align:left;mso-layout-grid-align:none;text-autospace:none'><span lang=EN-US style='font-size:12.0pt;font-family:Arial;mso-fareast-font-family:仿宋_GB2312;color:blue;mso-font-kerning:0pt'><![if !supportEmptyParas]> <![endif]><o:p></o:p></span></p><p class=MsoNormal align=left style='text-align:left;mso-layout-grid-align:none;text-autospace:none'><span lang=EN-US style='font-size:12.0pt;font-family:Arial;mso-fareast-font-family:仿宋_GB2312;color:blue;mso-font-kerning:0pt'>4.1 </span><spanstyle='font-size:12.0pt;font-family:仿宋_GB2312;color:blue;mso-font-kerning:0pt'>算法思想<spanlang=EN-US><o:p></o:p></span></span></p><p class=MsoNormal align=left style='text-align:left;mso-layout-grid-align:none;text-autospace:none'><span lang=EN-US style='font-size:10.0pt;font-family:仿宋_GB2312;color:black;mso-font-kerning:0pt'><![if !supportEmptyParas]> <![endif]><o:p></o:p></span></p><p class=MsoNormal align=left style='text-align:left;text-indent:20.0pt;mso-char-indent-count:2.0;mso-char-indent-size:10.0pt;mso-layout-grid-align:none;text-autospace:none'><span style='font-size:10.0pt;font-family:仿宋_GB2312;color:black;mso-font-kerning:0pt'>回溯（</span><span lang=EN-US style='font-size:10.0pt;mso-fareast-font-family:仿宋_GB2312;color:black;mso-font-kerning:0pt'>b ac k t r a c k i n g</span><span style='font-size:10.0pt;font-family:仿宋_GB2312;color:black;mso-font-kerning:0pt'>）是一种系统地搜索问题解答的方法。为了实现回溯，首先需要为问题定义一个解空间（ </span><spanlang=EN-US style='font-size:10.0pt;mso-fareast-font-family:仿宋_GB2312;color:black;mso-font-kerning:0pt'>solution space</span><span style='font-size:10.0pt;font-family:仿宋_GB2312;color:black;mso-font-kerning:0pt'>），这个空间必须至少包含问题的一个解（可能是最优的）。在迷宫老鼠问题中，我们可以定义一个包含从入口到出口的所有路径的解空间；在具有</span><i><spanlang=EN-US style='font-size:10.0pt;mso-fareast-font-family:仿宋_GB2312;color:black;mso-font-kerning:0pt'>n </span></i><span style='font-size:10.0pt;font-family:仿宋_GB2312;color:black;mso-font-kerning:0pt'>个对象的</span><spanlang=EN-US style='font-size:10.0pt;mso-fareast-font-family:仿宋_GB2312;color:black;mso-font-kerning:0pt'>0 / 1</span><span style='font-size:10.0pt;font-family:仿宋_GB2312;color:black;mso-font-kerning:0pt'>背包问题中（见</span><span⌨️ 快捷键说明
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