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Merged
merged 2 commits into from
Oct 2, 2017
Merged

add KMP algorithm; improve binary search #124

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85771ea
prevent (ub+lb) overflow
lvncnt Oct 1, 2017
79a73ae
KMP algorithm
lvncnt Oct 1, 2017
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55 changes: 55 additions & 0 deletions Misc/KMP.java
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Original file line number Diff line number Diff line change
@@ -0,0 +1,55 @@

/*
Implementation of Knuth–Morris–Pratt algorithm
Usage:
final String T = "AAAAABAAABA";
final String P = "AAAA";
KMPmatcher(T, P);
*/
public class KMP {

// find the starting index in string T[] that matches the search word P[]
public void KMPmatcher(final String T, final String P) {
final int m = T.length();
final int n = P.length();
final int[] pi = computePrefixFunction(P);
int q = 0;
for (int i = 0; i < m; i++) {
while (q > 0 && T.charAt(i) != P.charAt(q)) {
q = pi[q - 1];
}

if (T.charAt(i) == P.charAt(q)) {
q++;
}

if (q == n) {
System.out.println("Pattern starts: " + (i + 1 - n));
q = pi[q - 1];
}
}

}

// return the prefix function
private int[] computePrefixFunction(final String P) {
final int n = P.length();
final int[] pi = new int[n];
pi[0] = 0;
int q = 0;
for (int i = 1; i < n; i++) {
while (q > 0 && P.charAt(q) != P.charAt(i)) {
q = pi[q - 1];
}

if (P.charAt(q) == P.charAt(i)) {
q++;
}

pi[i] = q;

}

return pi;
}
}
2 changes: 1 addition & 1 deletion Searches/BinarySearch.java
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Original file line number Diff line number Diff line change
Expand Up @@ -23,7 +23,7 @@ public static <T extends Comparable<T>> int BS(T array[], T key, int lb, int ub)
if ( lb > ub)
return -1;

int mid = (ub+lb)/2;
int mid = (ub+lb) >>> 1;
int comp = key.compareTo(array[mid]);

if (comp < 0)
Expand Down