// see pseudocode https://en.wikipedia.org/wiki/Knuth%E2%80%93Morris%E2%80%93Pratt_algorithm#Description_of_pseudocode_for_the_search_algorithm
// \param T is the precomputed lookup table for the search string
public static int kmpSearch(IStringAccessor <int> S, IStringAccessor <int> W, int[] T, out bool found)
{
found = false;
int m = 0; // the beginning of the current match in S
int i = 0; // the position of the current character in W
while (m + i < S.length())
{
if (W.at(i) == S.at(m + i))
{
if (i == W.length() - 1)
{
found = true;
return(m);
}
i++;
}
else
{
if (T[i] > -1)
{
m = m + i - T[i]; i = T[i];
}
else
{
m++;
i = 0;
}
}
}
// if we reach here, we have serched all of S unsuccessfully
return(-1);
}
// see pseudocode https://en.wikipedia.org/wiki/Knuth%E2%80%93Morris%E2%80%93Pratt_algorithm#Description_of_pseudocode_for_the_table-building_algorithm
// \param W the word to be analyzed
// \param T the table to be filled
public static void kmpTable(IStringAccessor <int> W, ref int[] T)
{
if (W.length() != T.Length)
{
throw new Exception();
}
int pos = 2; // the current position we are computing in T
int cnd = 0; // the zero-based index in W of the next character of the current candidate substring
// the first few values are fixed but different fro what the algorithm might suggest
T[0] = -1;
T[1] = 0;
while (pos < W.length())
{
// first case: the substring continues
if (W.at(pos - 1) == W.at(cnd))
{
T[pos] = cnd + 1;
cnd++;
pos++;
}
// second case: it doesn't, but we can fall back)
else if (cnd > 0)
{
cnd = T[cnd];
}
// third case: we have run out of candidates. Note cnd = 0
else
{
T[pos] = 0;
pos++;
}
}
}
