算法导论-第32章-字符串匹配：有限自动机方法（改进版本：预处理阶段复杂度为O(m*| ∑ |) ）C++实现

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

void built_pai(char P[], int pai[], size_t m) {
int k{};
pai[0] = 0;
for (int q = 1; q < m; ++q) {
while (k > 0 && P[k] != P[q]) {
k = pai[k];
}
if (P[k] == P[q]) {
k++;
}
pai[q] = k;
}
}

void built_transform_function(int* theta, char* P, char* alpha, size_t m, size_t alpha_size) {
int* pai = new int[m] {};
built_pai(P, pai, m);
for (int i = 0; i < alpha_size; ++i) {
if (alpha[i] == P[0]) {
theta[i] = 1;
}
}
for (int i = 1; i <= m; ++i) {
for (int j = 0; j < alpha_size; ++j) {
if (P[i] == alpha[j]) {
theta[i * alpha_size + j] = i + 1;
}
else {
int tmp = pai[i - 1];
if (P[tmp] == alpha[j]) {
theta[i * alpha_size + j] = tmp + 1;
}
else if (alpha[j] == P[0]){
theta[i * alpha_size + j] = 1;
}
}
}
}
delete[]pai;
}

int find_index_of_alpha(char alpha[], char c, int alpha_size) {
for (int i = 0; i < alpha_size; ++i) {
if (alpha[i] == c) {
return i;
}
}
return -1;
}

void finite_automation_matcher(char T[], int theta[], char alpha[], int n, int m, int alpha_size) {
int q{};
for (int i = 0; i < n; ++i) {
q = theta[q * alpha_size + find_index_of_alpha(alpha, T[i], alpha_size)];
if (q == m) {
cout << "Pattern occures with shit " << i - m << endl;
}
}
}

int main(int argc, char* argv[]) {
vector<char> v{};
char element{};
cout << "please enter the sum of alphabet (end by '0') : " << endl;
while (cin >> element) {
if (element != '0') {
v.push_back(element);
}
else {
break;
}
}
size_t alpha_size{ v.size() };
char* alpha = new char[alpha_size] {};
int index{};
for_each(v.begin(), v.end(), [=](char x)mutable{ alpha[index++] = x; });
v.clear();
cout << "please enter the pattern (end by '0') : " << endl;
while (cin >> element) {
if (element != '0') {
v.push_back(element);
}
else {
break;
}
}
size_t m{ v.size() };
char* P = new char[m] {};
index = 0;
for_each(v.begin(), v.end(), [=](char x)mutable{ P[index++] = x; });
int* theta = new int[(m + 1) * alpha_size] {};
built_transform_function(theta, P, alpha, m, alpha_size);
v.clear();
cout << "please enter the text (end by '0') : " << endl;
while (cin >> element) {
if (element != '0') {
v.push_back(element);
}
else {
break;
}
}
size_t n{ v.size() };
char* T = new char
{};
index = 0;
for_each(v.begin(), v.end(), [=](char x)mutable{ T[index++] = x; });
for (int i = 0; i < n; ++i) {
cout << T[i] << " ";
}
cout << endl;
finite_automation_matcher(T, theta, alpha, n, m, alpha_size);
delete[]T;
delete[]P;
delete[]alpha;
return 0;
}