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Commit 585878f

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Add one more solution for StringTransformation task
1 parent ab1fcb5 commit 585878f

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3 files changed

+67
-16
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3 files changed

+67
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‎interview-materials/tasks.md‎

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@@ -19,22 +19,6 @@ Add operation with pets batch update (for example, add new field - owner).
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Propose algorithm for sorting a bunch of long strings situated on disk.
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We have restriction of RAM size: so only one string could be loaded into RAM simultaneously.
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## Make one string from another
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Написать метод, на вход которого приходит две строки.
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На выходе надо проверить, можно ли получить одну строку из другой за одно исправление:
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- замена одного символа в одной строке
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- вставка/удаление одного символа из одной строки
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Примеры тестовых сценариев:
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- first = "a", second = "b" -> true
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- first = "ab", second = "b" -> true
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- first = "ab", second = "cb" -> true
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- first = "ab", second = "ba" -> false
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- first = "abcd", second = "abd" -> true
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## Сортировки:
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- быстрая

‎src/main/java/by/andd3dfx/string/StringTransformation.java‎

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@@ -2,6 +2,8 @@
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import org.apache.commons.lang3.StringUtils;
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import static org.apache.commons.lang3.math.NumberUtils.min;
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/**
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* <pre>
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* Написать метод (класс и импорты не нужны) на вход которого приходит две строки.
@@ -67,4 +69,49 @@ private static boolean remainingPartsShouldBeEqual(String first, int from1, Stri
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second.substring(from2)
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);
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}
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public static boolean couldTransformUsingLevenshteinDistance(String first, String second) {
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return levenshteinDistance(first, second) <= 1;
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}
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/**
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* Use Wagner-Fisher algorithm. For details check
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* <a href="https://habr.com/ru/articles/676858/">article1</a>,
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* <a href="https://en.wikipedia.org/wiki/Wagner%E2%80%93Fischer_algorithm">article2</a>
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*
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* @param str1 First string
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* @param str2 Second string
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* @return Levenshtein distance
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*/
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public static int levenshteinDistance(String str1, String str2) {
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var m = str1.length();
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var n = str2.length();
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// for all i and j, d[i,j] will hold the distance between
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// the first i characters of s and the first j characters of t
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// note that d has (m+1)*(n+1) values
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var d = new int[m + 1][n + 1];
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// source prefixes can be transformed into empty string by
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// dropping all characters
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for (int i = 1; i <= m; i++) {
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d[i][0] = i;
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}
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// target prefixes can be reached from empty source prefix
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// by inserting every character
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for (int j = 1; j <= n; j++) {
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d[0][j] = j;
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}
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for (int j = 1; j <= n; j++) {
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for (int i = 1; i <= m; i++) {
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var substitutionCost = (str1.charAt(i - 1) == str2.charAt(j - 1)) ? 0 : 1;
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d[i][j] = min(d[i - 1][j] + 1, // deletion
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d[i][j - 1] + 1, // insertion
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d[i - 1][j - 1] + substitutionCost); // substitution
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}
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}
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return d[m][n];
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}
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}

‎src/test/java/by/andd3dfx/string/StringTransformationTest.java‎

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import org.junit.Test;
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import static by.andd3dfx.string.StringTransformation.couldTransform;
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import static by.andd3dfx.string.StringTransformation.couldTransformUsingLevenshteinDistance;
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import static org.assertj.core.api.Assertions.assertThat;
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public class StringTransformationTest {
@@ -12,32 +13,51 @@ public void couldTransform_changeOneChar() {
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assertThat(couldTransform("a", "b")).isTrue(); // change one char, 1-char string
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assertThat(couldTransform("a1b", "c1b")).isTrue(); // change one (first) char
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assertThat(couldTransform("a1b", "a1d")).isTrue(); // change one (last) char
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assertThat(couldTransformUsingLevenshteinDistance("a", "b")).isTrue(); // change one char, 1-char string
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assertThat(couldTransformUsingLevenshteinDistance("a1b", "c1b")).isTrue(); // change one (first) char
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assertThat(couldTransformUsingLevenshteinDistance("a1b", "a1d")).isTrue(); // change one (last) char
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}
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@Test
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public void couldTransform_removeOneChar() {
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assertThat(couldTransform("abcd", "bcd")).isTrue(); // remove one (first) char
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assertThat(couldTransform("abcd", "acd")).isTrue(); // remove one (inner) char
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assertThat(couldTransform("abcd", "abc")).isTrue(); // remove one (last) char
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assertThat(couldTransformUsingLevenshteinDistance("abcd", "bcd")).isTrue(); // remove one (first) char
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assertThat(couldTransformUsingLevenshteinDistance("abcd", "acd")).isTrue(); // remove one (inner) char
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assertThat(couldTransformUsingLevenshteinDistance("abcd", "abc")).isTrue(); // remove one (last) char
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}
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@Test
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public void couldTransform_addOneChar() {
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assertThat(couldTransform("bcd", "abcd")).isTrue(); // add one (first) char
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assertThat(couldTransform("abd", "abcd")).isTrue(); // add one (inner) char
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assertThat(couldTransform("abc", "abcd")).isTrue(); // add one (last) char
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assertThat(couldTransformUsingLevenshteinDistance("bcd", "abcd")).isTrue(); // add one (first) char
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assertThat(couldTransformUsingLevenshteinDistance("abd", "abcd")).isTrue(); // add one (inner) char
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assertThat(couldTransformUsingLevenshteinDistance("abc", "abcd")).isTrue(); // add one (last) char
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}
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@Test
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public void couldTransform_significantlyDifferentLengths() {
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assertThat(couldTransform("abcd", "ab")).isFalse();
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assertThat(couldTransform("bc", "abcd")).isFalse();
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assertThat(couldTransformUsingLevenshteinDistance("abcd", "ab")).isFalse();
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assertThat(couldTransformUsingLevenshteinDistance("bc", "abcd")).isFalse();
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}
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@Test
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public void couldTransform_transformIsNotPossible() {
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assertThat(couldTransform("ab", "ba")).isFalse(); // same lengths
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assertThat(couldTransform("abcde", "abdm")).isFalse(); // different lengths
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assertThat(couldTransform("abdm", "abcde")).isFalse(); // different lengths
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assertThat(couldTransformUsingLevenshteinDistance("ab", "ba")).isFalse(); // same lengths
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assertThat(couldTransformUsingLevenshteinDistance("abcde", "abdm")).isFalse(); // different lengths
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assertThat(couldTransformUsingLevenshteinDistance("abdm", "abcde")).isFalse(); // different lengths
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}
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}

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