Java Program for KMP Algorithm for Pattern Searching
Given a text txt[0..n-1] and a pattern pat[0..m-1], write a function search(char pat[], char txt[]) that prints all occurrences of pat[] in txt[]. You may assume that n > m.
Examples:
Input: txt[] = “THIS IS A TEST TEXT”
pat[] = “TEST”
Output: Pattern found at index 10
Input: txt[] = “AABAACAADAABAABA”
pat[] = “AABA”
Output: Pattern found at index 0
Pattern found at index 9
Pattern found at index 12
KMP Algorithm for Pattern Searching
Pattern searching is an important problem in computer science. When we do search for a string in notepad/word file or browser or database, pattern searching algorithms are used to show the search results.
Program for KMP Algorithm for Pattern Searching
Below is the implementation of KMP Algorithm:
Java
class KMP_String_Matching {
void KMPSearch(String pat, String txt)
{
int M = pat.length();
int N = txt.length();
int lps[] = new int [M];
int j = 0 ;
computeLPSArray(pat, M, lps);
int i = 0 ;
while (i < N) {
if (pat.charAt(j) == txt.charAt(i)) {
j++;
i++;
}
if (j == M) {
System.out.println( "Found pattern "
+ "at index " + (i - j));
j = lps[j - 1 ];
}
else if (i < N && pat.charAt(j) != txt.charAt(i)) {
if (j != 0 )
j = lps[j - 1 ];
else
i = i + 1 ;
}
}
}
void computeLPSArray(String pat, int M, int lps[])
{
int len = 0 ;
int i = 1 ;
lps[ 0 ] = 0 ;
while (i < M) {
if (pat.charAt(i) == pat.charAt(len)) {
len++;
lps[i] = len;
i++;
}
else
{
if (len != 0 ) {
len = lps[len - 1 ];
}
else
{
lps[i] = len;
i++;
}
}
}
}
public static void main(String args[])
{
String txt = "ABABDABACDABABCABAB" ;
String pat = "ABABCABAB" ;
new KMP_String_Matching().KMPSearch(pat, txt);
}
}
|
Output
Found pattern at index 10
Complexity of the above Method:
Time Complexity: O(m+n)
Space Complexity: O(m)
Please refer complete article on KMP Algorithm for Pattern Searching for more details!
Last Updated :
10 Jan, 2024
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