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Copy pathKMPAlgorithm.java
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72 lines (56 loc) · 1.76 KB
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public class KMPAlgorithm {
public static int kmpSearch(String text, String pattern) {
if (pattern == null || pattern.isEmpty()) return 0;
if (text == null || text.isEmpty()) return -1;
int n = text.length();
int m = pattern.length();
int[] lps = buildLPS(pattern);
int i = 0;
int j = 0;
while (i < n) {
if (text.charAt(i) == pattern.charAt(j)) {
i++;
j++;
}
if (j == m) {
return i - j;
} else if (i < n && text.charAt(i) != pattern.charAt(j)) {
if (j != 0) {
j = lps[j - 1];
} else {
i++;
}
}
}
return -1;
}
private static int[] buildLPS(String pattern) {
int m = pattern.length();
int[] lps = new int[m];
int len = 0;
int i = 1;
while (i < m) {
if (pattern.charAt(i) == pattern.charAt(len)) {
len++;
lps[i] = len;
i++;
} else {
if (len != 0) {
len = lps[len - 1];
} else {
lps[i] = 0;
i++;
}
}
}
return lps;
}
public static void main(String[] args) {
String text = "abxabcabcaby";
String pattern = "abcaby";
int index = kmpSearch(text, pattern);
System.out.println("Pattern found at index: " + index);
System.out.println("Pattern found at index: " + kmpSearch("hello", "ll"));
System.out.println("Pattern found at index: " + kmpSearch("aaaaa", "bba"));
}
}