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66 lines
2.2 KiB
Java
66 lines
2.2 KiB
Java
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import edu.princeton.cs.introcs.In;
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import edu.princeton.cs.introcs.StdOut;
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/*************************************************************************
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* Compilation: javac LongestCommonSubstring.java
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* Execution: java LongestCommonSubstring file1.txt file2.txt
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* Dependencies: SuffixArray.java StdOut.java In.java
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*
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* Reads in two text strings, replaces all consecutive blocks of
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* whitespace with a single space, and then computes the longest
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* common substring.
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*
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* Assumes that the character '\1' does not appear in either text.
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* Perhaps, search for a character that does not appear in either text
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* (and make sure SuffixArray.java doesn't choose the same one).
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*
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* % java LongestCommonSubstring tale.txt mobydick.txt
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* ' seemed on the point of being '
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*
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*************************************************************************/
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public class LongestCommonSubstring {
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public static void main(String[] args) {
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// read in two string from two files
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In in1 = new In(args[0]);
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In in2 = new In(args[1]);
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String text1 = in1.readAll().trim().replaceAll("\\s+", " ");
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String text2 = in2.readAll().trim().replaceAll("\\s+", " ");
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int N1 = text1.length();
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int N2 = text2.length();
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// concatenate two string with intervening '\1'
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String text = text1 + '\1' + text2;
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int N = text.length();
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// compute suffix array of concatenated text
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SuffixArray suffix = new SuffixArray(text);
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// search for longest common substring
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String lcs = "";
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for (int i = 1; i < N; i++) {
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// adjacent suffixes both from first text string
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if (suffix.index(i) < N1 && suffix.index(i-1) < N1) continue;
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// adjacent suffixes both from secondt text string
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if (suffix.index(i) > N1 && suffix.index(i-1) > N1) continue;
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// check if adjacent suffixes longer common substring
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int length = suffix.lcp(i);
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if (length > lcs.length()) {
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lcs = text.substring(suffix.index(i), suffix.index(i) + length);
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}
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}
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// print out longest common substring
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StdOut.println(lcs.length());
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StdOut.println("'" + lcs + "'");
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}
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}
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