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Copy pathKmpSubstringSearch.java
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71 lines (65 loc) · 2.12 KB
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package code;
public class KmpSubstringSearch {
KmpSubstringSearch(){
}
public static int[] longSuffPre(String pattern, int patternSize){
int[] lps = new int[patternSize];
int i=0,j=1;
while( j < pattern.length()){
//System.out.println(pattern.charAt(i) +" "+ pattern.charAt(j));
if(pattern.charAt(i) == pattern.charAt(j)){
lps[j] = i + 1;
i++;
}else {
if(i != 0) {
i = lps[i - 1];
j--;
}
}
j++;
}
return lps;
}
public static void main(String[] args){
String[] texts = {"abcxabcdabxabcdabcdabcy","adsgwadsxdsgwadsgz"};
String[] pats = {"abcdabcy","dsgwadsgz"/*"aabaabaaa"*/};
int i = 0;
for(String text : texts){
String pattern = pats[i++];
//System.out.println(pattern);
int[] lps = longSuffPre(pattern,pattern.length());
System.out.println(pattern +" exists in "+text+" at index "+substringSearch(text,pattern,lps));
}
//System.out.println("working");
}
private static int substringSearch(String text, String pattern, int[] lps){
int index = -1;
int flag = 0;
int i,j;
for(i=0,j=0;i<text.length();){
//System.out.println(text.charAt(i)+" "+ pattern.charAt(j));
if( text.charAt(i) != pattern.charAt(j) ){
//System.out.println(text.charAt(i)+" "+ pattern.charAt(j));
if( j != 0 ) {
j = lps[j-1];
flag = 0;
}else if(flag == 0){
i++;
}
}
if ( text.charAt(i) == pattern.charAt(j) ) {
flag = 1;
index = i - j;
i++;
j++;
}
}
return j==pattern.length() ? index : -1;
}
private static boolean prefixExists(int[] lps, int index) {
if( index != 0 && lps[index-1] != 0 ) {
return true;
}
return false;
}
}