public static long[] PreComputeHashes(
string T,
int P,
long p,
long x)
{
string last = T.Substring(T.Length - P);
long[] res = new long[T.Length - P + 1];
res[T.Length - P] = Q2HashingWithChain.PolyHash(last, 0, last.Length);
long pow = 1;
for (int i = 0; i < P; i++)
{
pow = (pow * x) % p;
}
for (int i = T.Length - P - 1; i >= 0; i--)
{
long firstChr = res[i + 1] * x;
long lastChr = pow * (long)T[i + P];
res[i] = (((T[i] + firstChr - lastChr) % p) + p) % p;
}
return(res);
}
public void PreComputeHashesTest()
{
// Uncomment the following line if you want to have it run
// Assert.Inconclusive();
string testStr = "aaaa";
int patternLen = 2;
long[] H = Q3RabinKarp.PreComputeHashes(
testStr, patternLen, 101, 3);
for (int i = 0; i < testStr.Length - patternLen + 1; i++)
{
long expectedHash =
Q2HashingWithChain.PolyHash(testStr, i, patternLen, 101, 3);
Assert.AreEqual(expectedHash, H[i]);
}
}
public long[] Solve(string pattern, string text)
{
long p = 1000000007;
long x = 263;
List <long> res = new List <long>();
Random t = new Random();
long pHash = Q2HashingWithChain.PolyHash(pattern, 0, pattern.Length);
long[] tHash = PreComputeHashes(text, pattern.Length, p, x);
for (int i = 0; i < tHash.Length; i++)
{
if (tHash[i] == pHash)
{
if (AreEqual(text, i, pattern))
{
res.Add(i);
}
}
}
return(res.ToArray());
}
