ACM模板——KMP算法

KMP

#include <string>
#include <iostream>
#include <cstring>
using namespace std;

void getfill(string s,int* f)
{
//memset(f,0,sizeof(f));  //根据其前一个字母得到
for(size_t i=1;i<s.size();i++)
{
int j=f[i];
while(j && s[i]!=s[j])
j=f[j];
f[i+1]=(s[i]==s[j])?j+1:0;
}
}

int KMP(string a,string s)
{
int* f=new int[s.size()+32];
memset(f,0,sizeof(int)*s.size());
getfill(s,f);size_t j=0;
for(size_t i=0;i<a.size();i++)
{
while(j && a[i]!=s[j])
j=f[j];
if(a[i]==s[j])
j++;
if(j==s.size()){
delete[] f;return i-s.size()+1;
}
}
delete[] f;
return -1;
}

KMP (int)

注: N为数组T的长度, M为数组P的长度. Next数组长度应稍大于P的长度

void MakeNext(int* P,int M,int* Next){
Next[0] = -1;
int i = 0, j = -1;
while(i<M){
if(j==-1||P[i]==P[j]){
i++,j++;
if(P[i]!=P[j])Next[i] = j;
else Next[i] = Next[j];
}
else j = Next[j];
}
}
int KMP(int* T,int N,int* P,int M)
{
MakeNext(P,M,Next);
int i=0,j=0;
while(i<N&&j<M){
if(T[i]==P[j]||j==-1)i++,j++;
else j = Next[j];
}
if(j==M)return i-M;
else return -2;
}