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filediff2(算法-用于VSS比较工具等).pdf
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上传时间: 2009-03-13
详细说明： The problem of determining the differences between two sequences of symbols has been studied extensively [1,8,11,13,16,19,20]. Algorithms for the problem have numerous applications, including spelling correction systems, file comparison tools, and the study of genetic evolution [4,5,17,18]. Formally, the problem statement is to find a longest common subsequence or, equivalently, to find the minimum ‘‘script’’ of symbol deletions and insertions that transform one sequence into the other. One of the earliest algorithms is by Wagne r & Fischer [20] and takes O(N2 ) time and space to solve a generalization they call the string-to-string correction problem. A later refinement by Hirschberg [7] delivers a longest common subsequence using only linear space. When algorithms are over arbitrary alphabets, use ‘‘equal—unequal’’ comparisons, and are characterized in terms of the size of their input, it has been shown that W(N2 ) time is necessary [1]. A ‘‘Four Russians’’ approach leads to slightly better O(N2 lglgN/lgN) and O(N2 /lgN) time algorithms for arbitrary and finite alphabets respectively [13]. The existence of faster algorithms using other comparison formats is still open. Indeed, for algorithms that use ‘‘less than—equal—greater than’’ comparisons, W(NlgN) time is the best lower bound known [9]. ...展开收缩
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