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94 lines
3.2 KiB
Java
94 lines
3.2 KiB
Java
package com.jwetherell.algorithms.strings;
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/**
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* Rotation of the string is some cyclic transformation of that string.
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* More formally a string s = uv is said to be a rotation of t if t = vu.
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* <p>
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* http://en.wikipedia.org/wiki/String_(computer_science)#Rotations
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* <br>
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* @Author Szymon Stankiewicz <mail@stankiewicz.me>
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* @author Justin Wetherell <phishman3579@gmail.com>
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*/
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public class Rotation {
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private static char charAt(String text, int pos) {
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pos = pos % text.length();
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return text.charAt(pos);
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}
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private static int compare(char a, char b, boolean greater) {
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if (a == b)
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return 0;
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return (a < b) ^ greater ? -1 : 1;
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}
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private static String bestRotation(String text, boolean greatest) {
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if (text.length() < 2)
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return text;
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final int n = text.length() * 2;
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int k = 0;
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int i = 0, j = 1;
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while (i + k < n && j + k < n) {
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final char a = charAt(text, i+k);
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final char b = charAt(text, j+k);
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final int comp = compare(a, b, greatest);
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if (comp == 0) {
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k++;
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} else if (comp > 0) {
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i += k+1;
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if (i <= j )
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i = j + 1;
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k = 0;
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} else {
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j += k+1;
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if (j <= i)
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j = i + 1;
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k = 0;
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}
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}
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final int pos = i < j ? i : j;
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return text.substring(pos) + text.substring(0, pos);
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}
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/**
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* Finds lexicographically minimal string rotation.
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* Lexicographically minimal string rotation is a rotation of a string possessing the
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* lowest lexicographical order of all such rotations.
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* Finding the lexicographically minimal rotation is useful as a way of normalizing strings.
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* <p>
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* http://en.wikipedia.org/wiki/Lexicographically_minimal_string_rotation
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* <br>
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* This function implements Duval's algorithm.
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* <br>
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* http://en.wikipedia.org/wiki/Lexicographically_minimal_string_rotation#Duval.27s_Lyndon_Factorization_Algorithm
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* Complexity: O(n)
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* <br>
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* @param text
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* @return lexicographicall minimal rotation of text
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*/
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public static String getLexicographicallyMinimalRotation(String text) {
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return bestRotation(text, false);
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}
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/**
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* Finds lexicographically maximal string rotation.
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* Lexicographically maximal string rotation is a rotation of a string possessing the
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* highest lexicographical order of all such rotations.
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* Finding the lexicographically maximal rotation is useful as a way of normalizing strings.
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* <p>
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* http://en.wikipedia.org/wiki/Lexicographically_minimal_string_rotation
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* <br>
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* This function implements Duval's algorithm.
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* http://en.wikipedia.org/wiki/Lexicographically_minimal_string_rotation#Duval.27s_Lyndon_Factorization_Algorithm
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* <br>
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* Complexity: O(n)
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* <br>
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* @param text
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* @return lexicographicall minimal rotation of text
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*/
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public static String getLexicographicallyMaximalRotation(String text) {
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return bestRotation(text, true);
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}
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}
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