C# 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
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.
C#
using System;
class GFG {
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[j] == txt[i]) {
j++;
i++;
}
if (j == M) {
Console.Write( "Found pattern "
+ "at index " + (i - j));
j = lps[j - 1];
}
else if (i < N && pat[j] != txt[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[i] == pat[len]) {
len++;
lps[i] = len;
i++;
}
else
{
if (len != 0) {
len = lps[len - 1];
}
else
{
lps[i] = len;
i++;
}
}
}
}
public static void Main()
{
string txt = "ABABDABACDABABCABAB" ;
string pat = "ABABCABAB" ;
new GFG().KMPSearch(pat, txt);
}
}
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Output:
Found pattern at index 10
Time Complexity: O(m+n)
Space Complexity: O(m)
Please refer complete article on KMP Algorithm for Pattern Searching for more details!
Last Updated :
08 Jun, 2022
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