一篇文章带你了解C++的KMP算法一篇文章带你了解C++的KMP算法

KMP算法

步骤1：先计算子串中的前后缀数组Next

C++代码：

步骤2：查找子串在母串中出现的位置。

总结

KMP算法 KMP算法作用：字符串匹配
例如母串S = “aaagoogleaaa”;

子串T= “google”;

步骤1：先计算子串中的前后缀数组Next

g	o	o	g	l	e
next[0]	next[1]	next[2]	next[3]	next[4]	next[5]
-1	0	0	0	1	0

C++代码：

//步骤1：void GetNext(string Tsub, vector& Next){int j = 0, k = -1; Next[0] = k; while (j < Tsub.length() - 1){if (k == -1 || Tsub[j] == Tsub[k]){Next[++j] = ++k; }else{k = Next[k]; }}}

步骤2：查找子串在母串中出现的位置。

//步骤2：int KMP(string S, string T, vector Next){int i = 0, j = 0; int m = S.length(); int n = T.length(); while (i < m && j < n){if (j == -1 || S[i] == T[j]){i++; j++; }else{j = Next[j]; }}if (j == n){return i - j; }else{return -1; }}

结合上面两个步骤写出完整代码：

#include #include using namespace std; //步骤1：void GetNext(string Tsub, vector& Next){int j = 0, k = -1; Next[0] = k; while (j < Tsub.length() - 1){if (k == -1 || Tsub[j] == Tsub[k]){Next[++j] = ++k; }else{k = Next[k]; }}}//步骤2：int KMP(string S, string T, vector Next){int i = 0, j = 0; int m = S.length(); int n = T.length(); while (i < m && j < n){if (j == -1 || S[i] == T[j]){i++; j++; }else{j = Next[j]; }}if (j == n){return i - j; }else{return -1; }}int main(){string S = "aaagoogleaaa"; string T = "google"; vector Next(T.length()); GetNext(T, Next); int retVal = KMP(S, T, Next); if (retVal == -1){std::cout << "can't Index" << std::endl; }else{std::cout << "Index :" << retVal << std::endl; }return 0; }

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