ITSA [C_ST42-易] 子字串出現次數

Problem

http://e-tutor.itsa.org.tw/e-Tutor/mod/programming/view.php?a=1376

Thinking

使用 KMP algo 去算匹配成功的次數, 至於KMP algo是什麼以我的功力目前還沒辦法解釋很清楚, 請google看高手解答

Solution

#include  
  
using namespace std;  
// KMP algo  
void next(string p, int *f){  
    f[0] = -1;  
    int j = -1;  
    for(int i = 1 ; i < p.length() ; i++){  
        while(j >= 0 && p[j + 1] != p[i])  
            j = f[j];  
          
        if(p[j + 1] == p[i])  
            j++;  
          
        f[i] = j;  
    }  
}  
int match(string T,string P, int *f){  
    int j = -1;  
    int matchNum = 0;  
      
    for(int i = 0 ; i < T.length() ; i++){  
        while(j >= 0 && P[j + 1] != T[i])  
            j = f[j];  
          
        if(P[j + 1] == T[i])  
            j++;  
          
        if(j == P.length() -1 ){  
            matchNum++;  
            j = f[j];  
        }  
    }  
    return matchNum;  
}  
int main(){  
    string T,P;  
      
    while(cin >> P >> T){  
        int *f = new int[P.length()];  
        f[0] = -1;  
        next(P,f);  
        cout << match(T, P, f) << endl;  
    }  
}