KMP算法代码&BF算法代码

BF算法是一种简单模式匹配算法BF算法，时间复杂度为O(m*n)。

KMP算法是一种改进的字符串模式匹配算法，时间复杂度为O(m+n).。

下面只贴出了代码，详细的算法介绍可参考任一本算法书籍或者该网页：http://www.cppblog.com/oosky/archive/2006/07/06/9486.html（该网页我没看过，百度来的，建议还是看算法书好了）。

注：KMP的代码基本是自己写的，get_next()函数是改进过的。BF代码直接从书上摘录的。参考书籍：《数据结构（C语言版）》

#include<iostream>using namespace std;void get_next(const char* t, int* next, int len);int index_KMP(const char* s,const char* t, int pos = 0);int index_BF(const char* s, const char* t, int pos = 0);int main(){const char* S = "dasdadsdsd";const char* T = "dasdasd";cout << "use BF:" << endl;int index = index_BF(S, T);if (index > -1)cout << T << " is a substring of " << S << " at index " << index + 1 << endl;elsecout << T << " is not a substring of " << S << endl;cout << "use KMP:" << endl;index = index_KMP(S, T);if (index > -1)cout << T << " is a substring of " << S << " at index " << index + 1 << endl;elsecout << T << " is not a substring of " << S << endl;return 0;}// O(m+n)int index_KMP(const char *S, const char *T, int pos){// 求T在主串S中第pos个字符之后的位置的KMP算法。// 其中，T非空，1 <= pos <= strlen(S)。int s_len = strlen(S);int t_len = strlen(T);if(t_len > s_len){return -1;}int *next = new int[t_len];get_next(T, next, t_len);// 获取模式串T的next值int count = 0;int i = pos, j = 0;while ((i < s_len) && (j < t_len)){if ((j == -1) || (S[i] == T[j])){++i;++j;}elsej = next[j];++count;}delete[] next;next = NULL;cout << "\nKMP loop count: " << count << endl;if (j >= t_len)return i - j;elsereturn -1;}void get_next(const char* t, int* next,int len){// 求模式串T的next函数修正值并存入数组next。int j = 0;      //求解每个next[j]next[0] = -1;   //递推基本条件,然后求解next[j+1]int k = -1;     //向后递推位置下标/*next[j]=k    =>T0...Tk-1=Tj-k...Tj-1求解next[j+1]1> 如果T0..Tk-1Tk=Tj-k...Tj-1Tj=>next[j+1]=k+1=next[j]+1;2>Tk<>Tj,next[k]=k', 如果Tj=Tk'=>next[j+1]=k'+1=next[k]+1=next[next[j]]+1;3>依次递推 最后情况next[j+1]=next[0]+1=0,即*/for (int condition = len - 1; j < condition;){if ((k == -1) || (t[j] == t[k]))  //k==-1证明已经与t[0]不匹配了，此时next[j+1]=0;{++j;++k;if (t[j] != t[k])next[j] = k;elsenext[j] = next[k];// 若Tj = Tk，则当主串中字符Si和Tj比较不等时，不需要再和Tk进行比较，// 而直接和TNext[k]进行比较，即此时的next[j]应和next[k]相同。//cout << "next[" << j << "]: " << next[j] << endl;}elsek = next[k];}}// O(m*n)int index_BF(const char* S, const char* T, int pos){// 返回子串T在主串S中第pos个字符之后的位置。若不存在，则函数值为0// 其中，T非空，0 <= pos < strlen(S)int s_len = strlen(S), t_len = strlen(T);int i = pos, j = 0;int count = 0;while (i < s_len && j < t_len){if (S[i] == T[j]){++i;++j;}else{i = i - j + 1;j = 0;}++count;}cout << "\nBF loop count: " << count << endl;if (j == t_len)return i - j;elsereturn -1;}