78 lines
2.2 KiB
Java
78 lines
2.2 KiB
Java
public class Main
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{
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// d is the number of characters in the input alphabet
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public final static int d = 256;
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/* pat -> pattern
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txt -> text
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q -> A prime number
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*/
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static void search(String pat, String txt, int q)
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{
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int M = pat.length();
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int N = txt.length();
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int i, j;
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int p = 0; // hash value for pattern
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int t = 0; // hash value for txt
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int h = 1;
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// The value of h would be "pow(d, M-1)%q"
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for (i = 0; i < M-1; i++)
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h = (h*d)%q;
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// Calculate the hash value of pattern and first
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// window of text
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for (i = 0; i < M; i++)
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{
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p = (d*p + pat.charAt(i))%q;
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t = (d*t + txt.charAt(i))%q;
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}
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// Slide the pattern over text one by one
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for (i = 0; i <= N - M; i++)
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{
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// Check the hash values of current window of text
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// and pattern. If the hash values match then only
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// check for characters on by one
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if ( p == t )
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{
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/* Check for characters one by one */
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for (j = 0; j < M; j++)
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{
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if (txt.charAt(i+j) != pat.charAt(j))
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break;
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}
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// if p == t and pat[0...M-1] = txt[i, i+1, ...i+M-1]
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if (j == M)
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System.out.println("Pattern found at index " + i);
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}
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// Calculate hash value for next window of text: Remove
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// leading digit, add trailing digit
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if ( i < N-M )
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{
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t = (d*(t - txt.charAt(i)*h) + txt.charAt(i+M))%q;
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// We might get negative value of t, converting it
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// to positive
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if (t < 0)
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t = (t + q);
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}
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}
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}
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/* Driver Code */
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public static void main(String[] args)
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{
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String txt = "ABCAMCABAMMAM";
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String pat = "AM";
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// A prime number
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int q = 101;
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// Function Call
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search(pat, txt, q);
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}
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} |