求目標(biāo)串中出現(xiàn)了幾個(gè)模式串

思路

一遭赂、構(gòu)建字典樹(shù)

二糯耍、構(gòu)建fail指針

三、串匹配

例題

HDU2222

#include <stdio.h>
#include <string.h>
#include <queue>
using namespace std;
namespace Trie{
    int next[500010][26], fail[500010], end[500010];//字典樹(shù)变抽，fail指針匕坯，單詞末尾標(biāo)記
    int root, L;//根節(jié)點(diǎn)，樹(shù)節(jié)點(diǎn)計(jì)數(shù)
    int new_node(){
        for(int i = 0; i < 26; i++){
            next[L][i] = -1;
        }
        end[L++] = 0;
        return L-1;
    }
    void init(){
        L=0;
        root = new_node();
    }
    void insert(const char buf[]){//建立字典樹(shù)
        int len = strlen(buf);
        int now = root;
        for(int i =0; i < len; i++){
            if(next[now][buf[i]-'a'] == -1){//這里默認(rèn)都是小寫(xiě)字母
                next[now][buf[i]-'a'] = new_node();
            }
            now = next[now][buf[i]-'a'];
        }
        end[now]++;
    }
    void build(){//構(gòu)建fail指針
        queue<int> que;
        fail[root] = root;
        for(int i = 0; i < 26; i++){
            if(next[root][i] == -1){
                next[root][i] = root;//指向root說(shuō)明沒(méi)有
            }else{
                fail[next[root][i]] = root;
                que.push(next[root][i]);
            }
        }
        while(!que.empty()){
            int now = que.front();
            que.pop();
            for(int i = 0; i < 26; i++){
                if(next[now][i] == -1){
                    next[now][i] = next[fail[now]][i]; //沒(méi)有這個(gè)字符就去fail骄崩，方便遍歷不用判斷是否空
                }else{
                    fail[next[now][i]] = next[fail[now]][i]; // 孩子的fail指針聘鳞，往自己fail方向找
                    que.push(next[now][i]);
                }
            }
        }
    }
    int query(const char buf[]){
        int len = strlen(buf);
        int now = root;
        int res = 0;
        for(int i = 0; i < len; i++){
            now = next[now][buf[i]-'a'];
            int temp = now;
            while(temp != root){
                res += end[temp];
                end[temp] = 0;
                temp = fail[temp];
            }
        }
        return res;
    }
}
char buf[1000010];
int main(){
    int t,n;
    scanf("%d",&t);
    while(t--){
        scanf("%d",&n);
        Trie::init();
        for(int i=0;i<n;i++){
            scanf("%s",buf);
            Trie::insert(buf);
        }
        Trie::build();
        scanf("%s",buf);
        printf("%d\n",Trie::query(buf));
    }
    return 0;
}