[C++]KMP算法实现

KMP算法说明：http://zh.wikipedia.org/wiki/%E5%85%8B%E5%8A%AA%E6%96%AF-%E8%8E%AB%E9%87%8C%E6%96%AF-%E6%99%AE%E6%8B%89%E7%89%B9%E7%AE%97%E6%B3%95

#include<string>

using namespace std;

class KMP
{
public:
    KMP(string);
    int search(string txt);

private:
    string pat;
    static const int R = 256;
    int* dfa[R];
    int M;
};

KMP::KMP(string _pat)
{
    pat = _pat;
    M = pat.length();
    for (int i = 0; i < R; i++){
        dfa[i] = new int[M];
        for (int j = 0; j < M; j++){
            dfa[i][j] = 0;
        }
    }
    dfa[pat[0]][0] = 1;
    for (int X = 0, j = 1; j < M; j++){
        for (int c = 0; c < R; c++){
            dfa[c][j] = dfa[c][X];
        }
        dfa[pat[j]][j] = j + 1;
        X = dfa[pat[j]][X];
    }
}

int KMP::search(string txt){
    int i, j;
    int N = txt.length();
    for (i = 0, j = 0; i < N&&j < M; i++){
        j = dfa[txt[i]][j];
    }
    if (j == M) //如果找到返回在txt中的位置
        return i - M;
    else        //找不到则返回txt的长度
        return N;
}

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