C ++程序执行基于有限状态自动机的搜索
这是一个C++程序，用于执行基于有限状态自动机的搜索。具有有限状态数的自动机称为有限自动机。在此，给文本一个text[0…t-1]并给出一个模式p[0...p-1]。我们必须在文本中找到模式，并将其所有出现的位置打印在相应的索引处。
演算法
Begin
Function void transitiontable():
1) put the entries in first row and filled it up. All entries in first row are always 0 except the entry for p[0] character. Always we need to go to state 1.
for p[0].
2) Initialize longestprefixsuffix as 0.
3) for i = 1 to P. (Here P is the length of the pattern)
a) Copy the entries from the row at index equal to longestprefixsuffix.
b)更新条目 for p[i] character to i+1.
c) Update longestprefixsuffix = TF[lps][pat[i]]
where TT is the 2D array.
End示例
#include<iostream>
#include<cstring>
#define NO_OF_CHARS 512
using namespace std;
//建立一个TF表，该表代表给定模式的有限自动机
void transitiontable(char *p, int P, int TT[][NO_OF_CHARS]) {
int i, longestprefixsuffix = 0, y;
//将条目放在第一行
for (y =0; y < NO_OF_CHARS; y++)
TT[0][y] = 0;
TT[0][p[0]] = 1;
//将条目放入其他行
for (i = 1; i<= P; i++) { // Copy values from row at index longestprefixsuffix
for (y = 0; y < NO_OF_CHARS; y++)
TT[i][y] = TT[longestprefixsuffix][y];
//更新条目
TT[i][p[i]] = i + 1;
//更新lps以填充下一行
if (i < P)
longestprefixsuffix = TT[longestprefixsuffix][p[i]]; // TT is the 2D array which is being constructed.
}
}
//在文本中打印所有出现的图案
void patternsearch(char *p, char *t) {
int P = strlen(p);
int T = strlen(t);
int TT[P+1][NO_OF_CHARS];
transitiontable(p, P, TT);
//通过FA处理文本。
int i, j=0;
for (i = 0; i < T; i++) {
j = TT[j][t[i]];
if (j == P) {
cout<<"\n pattern is found at index: "<< i-P+1;
}
}
}
int main() {
char *text = "AABAA ABBAACCDD CCDDAABAA"; //take the text as input
char *pattern = "AABAA"; //take the pattern as input
patternsearch(pattern, text);
getchar();
return 0;
}输出结果
pattern is found at index: 0 pattern is found at index: 20