kmp算法

#include<bits/stdc++.h>
using namespace std;
typedef long long LL;
typedef maxn = 1000005;
#define iss ios::sync_with_stdio(false)
int ans = 0;
char a[maxn],b[maxn];
int Next[maxn];
void getnext(char b[]){
    int i,j,len=strlen(b);
    Next[0]=-1;
    for(i=0,j=-1;i<len;)
    if(j==-1||b[i]==b[j]) Next[++i]=++j;
    else j=Next[j];
}
void kmp(char a[],char b[]){
    int i,j,n,len;
    getnext(b);
    n=strlen(a);
    len=strlen(b);
    for(i=j=0;i<n;){
        if(j==-1||a[i]==b[j]) i++,j++;
        else  j=Next[j];        
        if(j >= len) ++ans,j = Next[j];
    }
}
int main(){
    iss;
    int n;
    cin>>n;
    while(n--){
        ans = 0;
        cin>>b>>a;
        kmp(a,b);
        cout<<ans<<endl;
    }

}

改进getnext

void getnext(char b[]){
    int i,j,len=strlen(b);
    Next[0]=-1;
    for(i=0,j=-1;i<len;)
    if(j==-1||b[i]==b[j]){
        ++i; ++j;
        if(b[i] != b[j]) Next[i] = j;
        else Next[i] = Next[j];
    }
    else j=Next[j];
}