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fix(searches): avoid int overflow and short-text crash in RabinKarpAlgorithm #7665

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fix(searches): avoid int overflow and short-text crash in RabinKarpAlgorithm #7665

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11 changes: 8 additions & 3 deletions src/main/java/com/thealgorithms/searches/RabinKarpAlgorithm.java
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Original file line number Diff line number Diff line change
Expand Up @@ -13,9 +13,14 @@ public static int search(String pattern, String text, int primeNumber) {
int index = -1; // -1 here represents not found
int patternLength = pattern.length();
int textLength = text.length();
int hashForPattern = 0;
int hashForText = 0;
int h = 1;
if (patternLength > textLength) {
return index;
}

// long, so hash * ALPHABET_SIZE cannot overflow for large primes such as 1_000_000_007
long hashForPattern = 0;
long hashForText = 0;
long h = 1;

// The value of h would be "pow(d, patternLength-1)%primeNumber"
for (int i = 0; i < patternLength - 1; i++) {
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2 changes: 1 addition & 1 deletion src/test/java/com/thealgorithms/searches/RabinKarpAlgorithmTest.java
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Expand Up @@ -8,7 +8,7 @@
class RabinKarpAlgorithmTest {

@ParameterizedTest
@CsvSource({"This is an example for rabin karp algorithmn, algorithmn, 101", "AAABBDDG, AAA, 137", "AAABBCCBB, BBCC, 101", "AAABBCCBB, BBCC, 131", "AAAABBBBCCC, CCC, 41", "ABCBCBCAAB, AADB, 293", "Algorithm The Algorithm, Algorithm, 101"})
@CsvSource({"This is an example for rabin karp algorithmn, algorithmn, 101", "AAABBDDG, AAA, 137", "AAABBCCBB, BBCC, 101", "AAABBCCBB, BBCC, 131", "AAAABBBBCCC, CCC, 41", "ABCBCBCAAB, AADB, 293", "Algorithm The Algorithm, Algorithm, 101", "nzdjsjggwx, jggw, 1000000007", "AB, ABC, 101"})
void rabinKarpAlgorithmTestExample(String txt, String pat, int q) {
int indexFromOurAlgorithm = RabinKarpAlgorithm.search(pat, txt, q);
int indexFromLinearSearch = txt.indexOf(pat);
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