When building the partial match table for KMP:
void buildBackTable() {
int i = 0, j = -1; b[0] = -1;
while (i < m) {
while (j >= 0 && P[i] != P[j]) j = b[j]; //Why is this a while loop!?
i++; j++;
b[i] = j;
}
}
How come that second while loop is not a conditional instead? Such as:
void buildBackTable() {
int i = 0, j = -1; b[0] = -1;
while (i < m) {
if (j >= 0 && P[i] != P[j]) j = b[j]; //Why not?
i++; j++;
b[i] = j;
}
}
In most of the examples I've tried, this statement is used to reset j to -1 when there is no match, so when the next iteration comes, we compare the first character of the string (P[j]) with the character at position i (P[i]). Is there an example where the while loop would be needed? I would love to see one. I've tried several samples of my own and changing the statement to a conditional would not make a difference (hence my question).
