KMP算法之一

#include <iostream>        //KMP算法是一种改进的字符串匹配算法，复杂度为O(n)
using namespace std;
char A[500000],B[500000];    //A是主串,B是子串,查询B串在A串的哪些地方出现
int n,m,next[500000];        //n,m分别是A，B的串长度，注意A，B的下标是从1开始的
void get_next()
{
    next[1]=0;
    int j=0;
    for(int i=2;i<=m;++i)
    {
        while(j>0&&B[j+1]!=B[i])
            j=next[j];
        if(B[j+1]==B[i])
            j=j+1;
        next[i]=j;
    }
}
void kmp()
{
    int j=0;
    for(int i=1;i<=n;++i)
    {
        while(j>0&&B[j+1]!=A[i])
            j=next[j];
        if(B[j+1]==A[i])
            j=j+1;
        if(j==m)
        {
            cout<<"Pattern occurs with shift  "<<i-m<<endl; 
            j=next[j];
        }
    }
    cout<<endl;
}
int main()
{
    while(scanf("%s %s",A+1,B+1)!=EOF)
    {
        for(n=0;A[n+1]!='\0';++n);
        for(m=0;B[m+1]!='\0';++m);
        get_next();
        kmp();
    }
    return 0;
}

//http://www.matrix67.com/blog/archives/115

/*
sample:

ababaab        (A串)
ab            (B串)
Pattern occurs with shift  0
Pattern occurs with shift  2
Pattern occurs with shift  5


*/