class KMP {
String string;
String pattern;
int[] lps;
KMP(String string, String pattern) {
this.string = string;
this.pattern = pattern;
this.lps = new int[pattern.length()];
}
public int kmp() {
this.createLPS();
int i = 0, j = 0;
while (i < this.string.length() && j < this.pattern.length()) {
if (this.string.charAt(i) == this.pattern.charAt(j)) {
i++;
j++;
} else if (j == 0) {
i++;
} else {
j = this.lps[j - 1];
}
}
if (j == pattern.length()) {
return i - pattern.length();
}
return -1;
}
private void createLPS() {
int i = 0, j = 1;
this.lps[0] = 0;
while (j < this.pattern.length()) {
if (this.pattern.charAt(i) == this.pattern.charAt(j)) {
this.lps[j] = i + 1;
i++;
j++;
} else if (i == 0) { //this is same as because we wont reach this part if they are not equal, this.pattern.charAt(i) != this.pattern.charAt(j) && i ==0
this.lps[j] = 0;
j++;
} else {
i = this.lps[i - 1];
}
}
}
}
public class Main {
public static void main(String args[]) {
String s = "abcabcabd";
String pattern = "abcabd";
KMP kmp = new KMP(s, pattern);
System.out.println(kmp.kmp());
}
}