KMP prefix table

Question

I am reading about KMP for string matching.
It needs a preprocessing of the pattern by building a prefix table.
For example for the string ababaca

Answer 1

Python Implementation

p='ababaca'

l1 = len(p)

j = 0
i = 1
prefix = [0]

while len(prefix) < l1:
    if p[j] == p[i]:
        prefix.append(j+1)
        i += 1
        j += 1
    else:
        if j == 0:
            prefix.append(0)
            i += 1
        if j != 0:
            j = prefix[j-1]

print prefix