KMP、扩展KMP、Manacher模板

推导过程推荐看这篇：

KMP模板：

void init(){
    int j = nex[0] = -1, i = 0;
    int len = strlen(str);
    while(i < len){
        if(j == -1 || str[i] == str[j]){
            nex[++i] = ++j;
        }else j = nex[j];
    }
}
int KMP(){
    int i  = 0, j = 0, sum = 0;
    int len = strlen(str), len1 = strlen(str1);
    while(j < len1){
        if(i == -1 || str[i] == str1[j]){
            i++;j++;
        }else i = nex[i];
        if(i == len) sum++;
    }
    return sum;
}

 推导详细过程推荐看这篇，通俗易懂：

扩展KMP模板：

void init(){
    int len = strlen(str1),a,p;
    nex[0] = len;
    for(int i = 1, j = -1; i < len; i ++, j--){
        if(j < 0 || i+nex[i-a] >= p){
            if(j < 0)
                p=i,j=0;
            while(p < len && str1[p]==str1[j])
                p++,j++;
            nex[i] = j;
            a = i;
        }else nex[i] = nex[i-a];
    }
}
void EKMP(){
    int a,p;
    int len = strlen(str), len1 = strlen(str1);
    for(int i = 1, j = -1; i < len; i++,j--){
        if(j<0 || i+nex[i-a] >= p){
            if(j < 0)
                p=i,j=0;
            while(p < len && str[p]==str1[j])
                p++,j++;
            extend[i] = j;
            a = i;
        }else extend[i] = nex[i-a];
    }
}

 这个推导过程较简单，网上很多博客都可以快速看懂的。

Manacher模板：

int Manacher(){
    int ans = 0, id = 0, len = strlen(str);
    for(int i = len; i >= 0; i --){
        str[i+i+2] = str[i];
        str[i+i+1] = '#';
    }
    str[0] = '*';
    for(int i = 2; i<2*len+1; i ++){
        if(p[id] + id > i) p[i] = min(p[2*id-i],p[id]+id-i);
        else p[i] = 1;
        while(str[i-p[i]] == str[i+p[i]])++p[i];
        if(p[id] + id < p[i]+i) id = i;
        if(ans < p[i]) ans = p[i];
    }
    return ans-1;
}