Boyer Moore k-mismatches algorithm fails

Question

I've done a program for string comparison with one mismatch at a programming website. It gives me wrong answer. I've working on it extensively but, I couldn't find testcases where my code fails. Can somebody provide me test cases where my code fails. I've done the comparison using Boyer Moore Horspool k-mismatches algorithm as it's the fastest searching algorithm

The code is as such

int BMSearch_k(string text, string pattern, int tlen, int mlen,int pos)
{    
int i, j=0,ready[256],skip2[256][mlen-1],neq;

for(i=0; i<256; ++i) ready[i] = mlen;
for(int a=0; a<256;a++) {
    for(i = mlen;i>mlen-k;i--)
    skip2[i][a] = mlen;
}    

for(i = mlen-2;i>=1;i--)    {
    for(j=ready[pattern[i]]-1;j>=max(i,mlen-k);j--)
        skip2[j][pattern[i]] = j-i;
    ready[pattern[i]] = max(i,mlen-k);
}

j = mlen-1+pos;
//cout<<"\n--jafffa--\n"<<pos<<"+"<<mlen<<"="<<j<<endl;
while(j<tlen+k) {
    //cout<<"\t--"<<j<<endl;
    int h = j;
    i=mlen-1;
    int neq=0,shift = mlen-k;

    while(i>=0&&neq<=k)    {
        //cout<<"\t--"<<i<<endl;
        if(i>=mlen-k)
            shift = min(shift,skip2[i][text[h]]);
        if(text[h]!= pattern[i])
            neq++;
        i--;
        h--;
    }
    if(neq<=k)
        return j-1;
    j += shift;
}

return -1;
}

Answer 1

You aren't initialising your arrays correctly,

int i, j=0,ready[256],skip2[256][mlen-1],neq;

for(i=0; i<256; ++i) ready[i] = mlen;
for(int a=0; a<256;a++) {
    for(i = mlen;i>mlen-k;i--)
    skip2[i][a] = mlen;
}

On the one hand, you declare skip2 as a 256×(mlen-1) array, on the other hand, you fill it as a (mlen+1)×256 array.

In the next loop,

for(i = mlen-2;i>=1;i--)    {
    for(j=ready[pattern[i]]-1;j>=max(i,mlen-k);j--)
        skip2[j][pattern[i]] = j-i;
    ready[pattern[i]] = max(i,mlen-k);
}

you use ready[pattern[i]] before it has been set. I don't know if those mistakes are what's causing the failing testcase, but it's easily imaginable that they do.