此代码适用于我从此处引用的 Aho-Corasick 算法
我理解这段代码直到 push_links 方法的 if 块,但我没有得到相同方法的 else 部分的用途或要求。更具体地说,第一种方法用于构建 trie。剩下的工作是通过第二种方法完成的,即将节点链接到它们最长的正确后缀,这些后缀也是某种模式的前缀。这是由 If 块执行的,那么 else 部分需要什么。
请帮助我。
const int MAXN = 404, MOD = 1e9 + 7, sigma = 26;
int term[MAXN], len[MAXN], to[MAXN][sigma], link[MAXN], sz = 1;
// this method is for constructing trie
void add_str(string s)
{
// here cur denotes current node
int cur = 0;
// this for loop adds string to trie character by character
for(auto c: s)
{
if(!to[cur][c - 'a'])
{
//here two nodes or characters are linked using transition
//array "to"
to[cur][c - 'a'] = sz++;
len[to[cur][c - 'a']] = len[cur] + 1;
}
// for updating the current node
cur = to[cur][c - 'a'];
}
//for marking the leaf nodes or terminals
term[cur] = cur;
}
void push_links()
{
//here queue is used for breadth first search of the trie
int que[sz];
int st = 0, fi = 1;
//very first node is enqueued
que[0] = 0;
while(st < fi)
{
// here nodes in the queue are dequeued
int V = que[st++];
// link[] array contains the suffix links.
int U = link[V];
if(!term[V]) term[V] = term[U];
// here links for the other nodes are find out using assumption that the
// link for the parent node is defined
for(int c = 0; c < sigma; c++)
// this if condition ensures that transition is possible to the next node
// for input 'c'
if(to[V][c])
{
// for the possible transitions link to the reached node is assigned over
// here which is nothing but transition on input 'c' from the link of the
// current node
link[to[V][c]] = V ? to[U][c] : 0;
que[fi++] = to[V][c];
}
else
{
to[V][c] = to[U][c];
}
}
}