61 lines
1.8 KiB
Java
61 lines
1.8 KiB
Java
package com.jwetherell.algorithms.sequence;
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/**
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* Finds the number of times a string occurs as a subsequence in a text.
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* <p>
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* http://www.geeksforgeeks.org/find-number-times-string-occurs-given-string/
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* <br>
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* @author Justin Wetherell <phishman3579@gmail.com>
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*/
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public class SubsequenceCounter {
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private static char[] seq = null;
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private static char[] subseq = null;
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private static int[][] tbl = null;
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private SubsequenceCounter() { }
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/**
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* Finds the number of times a string occurs as a subsequence in a text.
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*
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* @param sequence Text to find subsequence in.
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* @param subSequence subsequence to find in the text.
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* @return Number of times a string occurs as a subsequence in a text
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*/
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public static int getCount(char[] sequence, char[] subSequence) {
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try {
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seq = sequence;
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subseq = subSequence;
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tbl = new int[seq.length + 1][subseq.length + 1];
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for (int row = 0; row < tbl.length; row++)
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for (int col = 0; col < tbl[row].length; col++)
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tbl[row][col] = countMatches(row, col);
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return tbl[seq.length][subseq.length];
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} finally {
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seq = null;
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subseq = null;
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tbl = null;
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}
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}
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private static int countMatches(int seqDigitsLeft, int subseqDigitsLeft) {
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if (subseqDigitsLeft == 0)
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return 1;
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if (seqDigitsLeft == 0)
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return 0;
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final char currSeqDigit = seq[seq.length - seqDigitsLeft];
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final char currSubseqDigit = subseq[subseq.length - subseqDigitsLeft];
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int result = 0;
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if (currSeqDigit == currSubseqDigit)
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result += tbl[seqDigitsLeft - 1][subseqDigitsLeft - 1];
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result += tbl[seqDigitsLeft - 1][subseqDigitsLeft];
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return result;
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}
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}
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